Changing Injection Quantity (IQ) is easy. Here’s how to do it.

Cable/Software/Port Setup

This how-to assumes that you’ve got your VAG-COM, downloaded the software, and made sure your car can connect to your computer. If you haven’t done this yet, www.ross-tech.com has detailed instructions.

Checking and Changing IQ

You car has to be running to get an accurate injection quantity reading. And it has to be up to operating temperature. So it’s best to drive the car for 20 minutes or so, some of it at highway speeds, to make sure you’ll get a good reading. You should not run your A/C during this test, as it will affect readings.

The screen prints in this article are from a 1997 VW Jetta TDI. If you have a different TDI some of the data displayed may be slightly different, so keep that in mind as you proceed.

You’ll first see this screen:

This is where VAG-COM launches. Click on the button named Select under the the words “Select Control Module.” Next you’ll see this screen:

All the engine control modules are listed, even if your car doesn’t have some of them, such as ABS. Click on 01-Engine to proceed and you’ll see something like the following screen:

The engine data will take a moment to populate. Newer cars populate faster than older ones (slower ECUs). Once the screen is populated, you can click on Login-11 to first login:

Type the numbers 12233 into the box to the right of the words Enter Code and click on Do It! This will take you back to the Engine screen:

This time click on the button Adaptation – 10. Next the screen below will appear:

However, you’ll see channel 00. Click the Up button to Channel 01 and you’ll see Adaptation numbers.

At the top of the screen you’ll see RPM and Injection Quantity. The IQ will most likely be a number between 1.0 and 3.0.

Next, look at the numbers on the left side of the screen. Below the Channel window you’ll see two boxes, one titled Stored Value and the other titled New Value. The default stored value is 32768. If your IQ has been previously adjusted you may see a different number. There’s a limit on the number range for IQ, it varies by ECU, but is approximately between 32645 and 32786.

The IQ measurement numbers are slightly counter-intuitive. A higher Injection Quantity (such as 3.0), will flow less fuel than a lower quantity (such as 2.0). And a lower new value (such as 32725 instead of the default 32768) will flow less fuel than a higher new value.

Why change Injection Quantity?

If your car:

• Smokes more than you want
• Shudders at slow down or idle

You may want to reduce fueling (increase the IQ number)

If your car is low on power, you may want to increase the IQ number.

Changing IQ

Here’s how to do it. On the adaptation screen, shown below:

Click into the New Value box and type in a new number. If the stored value is 32768 and you want to reduce fueling, try a lower number such as 32750 or 32725. Click on Test at the bottom of the screen. The IQ number will change (and your engine tone will change, too). Look at the new Injection Quantity at the top of the screen and see if it’s what you want. You can further adjust the IQ by typing in a new number and clicking on Test, or by using the up and down buttons to the right of the New Value box.

Once you’re satisfied with the IQ and want to test drive the car to gauge results, click on Save at the bottom of the screen:

You’ll be asked, Are You SURE?

Click on Yes to save the new setting. If you want, you can drive the car with the computer hooked up to determine if you’ve achieved the result you were after (more power, less shudder), and further adjust the IQ if needed.

Once you’re satisfied, click on Done, Go Back at the bottom of the screen, Back on the engine screen, and Exit on the main screen to exit VAG-COM.

Done!

One of the most basic VAG-COM uses is checking timing after a timing belt change. We’ll walk through that process here. In addition, adjusting your timing to be slightly (or more) advanced can improve cold starting, accelerator response, and fuel economy. So there are a lot of good reasons to have your timing set properly.

Here’s how to check.

Cable/Software/Port Setup

This how-to assumes that you’ve got your VAG-COM, downloaded the software, and made sure your car can connect to your computer. If you haven’t done this yet, www.ross-tech.com has detailed instructions.

Checking Timing

You car has to be running to check the timing. And it has to be up to operating temperature. VAG-COM also measures fuel temperature, and will provide slightly different readings if the fuel is cold. So it’s best to drive the car for 20 minutes or so, some of it at highway speeds, to make sure you’ll get a good reading.

The screen prints in this article are from a 1997 VW Jetta TDI. If you have a different TDI some of the data displayed may be slightly different, so keep that in mind as you proceed.

You’ll first see this screen:

This is where VAG-COM launches. Click on the button named Select under the the words “Select Control Module.” Next you’ll see this screen:

All the engine control modules are listed, even if your car doesn’t have some of them, such as ABS. Click on 01-Engine to proceed and you’ll see something like the following screen:

The engine data will take a moment to populate. Newer cars populate faster than older ones (slower ECUs). Once the screen is populated, you can click on Basic Settings-04 to see the timing data, shown below:

When this screen appears you won’t see the blocks with timing data as shown above. Hit the Enter key on your laptop for this data to display, or click the Up button under the Group label to Group one, and then click back Down to Group 000 to display the timing.

The data you’re after is in Block 2. In the sample screen it shows a timing setting of 64. Although the measurements vary by vehicle, this timing is advanced but within spec for most TDIs. If you want to see a graph click on the TDI-Timing button on the lower right of the screen and you’ll see the following:

This screen shows several pieces of data.

• The Red, Blue, and Green lines show the limits of timing within spec, from most retarded (red), to normal (blue) to advanced (green). The yellow line shows how the timing is set on your car. In this example it’s advanced, but within specifications.
• You’ll see fuel temp in the lower left of the screen. It shows 95F here. If the fuel is too cold you’ll see a warning message at the bottom of the graph.
• Also at the bottom of the graph you’ll see Result. In this case it says Timing within spec slightly advanced.
• However, on the right side of the graph you’ll see a drop down box where you can select the engine that most closely matches your car. And in this case you can see a 1.7l R4 SDI selected, not the 1Z/AHU that an A3 Jetta has. So the graph is calibrated for an engine different than the one in the sample car. You should choose a graph that most closely matches your engine (which we failed to do here) to get the most accurate data on your car’s timing

What do I do with the data?

As previously mentioned, timing settings can affect starting, power, and fuel economy. And timing that is way off can potentially damage your engine.

If you don’t see any data on the graph, or if your timing number is over 150, your timing may not have been set properly when your car was serviced. Your timing belt may be off at tooth, or even two.

The ECU will do its best to correct timing issues when the engine is running over 1600 RPM. Since the timing measurement is taken at idle, you won’t see any ECU correction in the screens above. And the ECU cannot compensate for retarded timing in during a cold start.

Correcting Timing

In rotary pump cars, timing should be set mechanically, not in VAG-COM. Tuners will fine-tune timing in VAG-COM, but it’s generally accepted that the best way to set timing is by changing pump position (1Z and AHU) and the pump cam (ALH). Timing can be fine-tuned in VAG-COM in Pumpe Deuse TDIs, which will be the subject of a future article.

Choosing between a stock or bigger turbo

Deciding whether to replace your turbo with another one just like it or to upgrade can be a complex decision. Or, it might be easy, because there may not be a larger turbo available that will easily fit your TDI. If there are upgrades available for our car, you should consider:

• A bigger turbo may not provide more power unless you make other upgrades (chip tuning, more fuel, better breathing)
• Bigger turbos may require supporting hardware for an easy install that can add to the replacement cost
• With larger turbos many expensive modifications may be required to take full advantage of the turbo’s potential

For example, a VNT-17 on an A4 TDI is a solid, well known upgrade. But it requires a $200 hose or a $100 adapter to fit stock intercooler piping. And bigger injectors (about $300), a chip tune ($300-700+), downpipe ($300-400), and improved intake (costs vary) are required to take full advantage of the power it supplies. And of course you’ll need a clutch. So you can see that choosing a bigger turbo is just the tip of the iceberg.

Many people consider a bigger turbo in hopes of improved reliability. And there are situations, even in stock cars (such as high altitudes) where a bigger turbo may last longer than the OE turbo, so this is a valid consideration.

Limited selection for some TDIs

For some TDIs there are very few options. For others, there are many. Let’s deal with the ones where choice is limited first.

• A5 Jetta, engine code BRM: Your option right now is a stock replacement turbo from VW, or a custom fabrication of manifold and turbo. No plug-and-play turbos that fit this car are in the US aftermarket—yet. With the A5 VW switched the turbo configuration to a top mount (the turbo sits on top of the manifold, not hanging below it as in earlier cars), so turbos from other TDIs won’t fit.
• B5.5 Passat, engine code BHW: This TDI has a separate turbo and manifold. Although there are probably many turbos that can be made to fit, the VNT-17, or Garrett 1749VA, is the only true plug-and-play option that’s readily available. Fortunately this is a great turbo, makes good power, and fails infrequently.



• A3/B4 TDIs, engine codes 1Z and AHU. These early TDIs had wastegate turbos in the US, not the variable vane turbos that are on all later VW TDIs. These two engines are nearly identical, but the 1Z has a Garrett turbo, the AHU has a Borg-Warner. The turbos are interchangeable. Like the B5.5 Passat, these turbos are separate from the manifold. There are other options for these cars including hybrid turbos with larger internals (plug-and-play), and switching to a VNT-15 or larger variable vane turbo (not plug-and-play).

A4 chassis TDIs, lots of options

On 1999.5-2006 A4 platform Golf, Jetta, and New Beetle, there are many turbo options. We’ll limit our discussion here to variable vane turbos with integrated exhaust manifolds. More than a few TDI owners have built their own manifolds, and there are also A4 TDIs out there with wastegate turbos. However, most daily drivers prefer the responsiveness of a variable vane turbo, and don’t want to go to the expense of building a manifold.

Stock Replacements

The ALH engined A4s (rotary pump) came with Garrett’s VNT-15 turbo. A version of this turbo started its life in the A3, but was first sold with an integrated manifold for the ALH engine. It’s very responsive, quite durable (especially if synthetic oil is used throughout its life) and makes great power. The dyno below shows what a VNT-15 can do with a chip and other supporting modifications. And when this dyno was run the turbo had 150K on it.

IBW dyno

The VNT-15 has benefited from running upgrades to vanes, internal metals, and other improvements during its life. It is less prone to carbon clogging (a common cause of failure on gently driven TDIs) than it was in the past. And many owners are out there with over 200K on their original turbos, so they do last.

When the Pumpe Deuse A4 chassis TDIs (engine code BEW) were brought to the US in 2004, VW switched from the Garrett VNT-15 to the Borg-Warner KP-39. This turbo is physically smaller than the VNT-15, but works exceptionally well in both stock and chip-tuned TDIs. 150 HP/240 lb/ft. is possible with this turbo and the right tune. The KP-39 does seem more prone to boost spikes than the VNT-15, especially in modified cars. And they also seem more stressed at high altitudes. Finally, some owners (again, in modified cars) have experienced boost creep at high speeds, eventually sending the car into limp mode. But these problems are neither that common nor catastrophic.

KP-39s just became available in the aftermarket. Because there was such a long delay before they were released, Garrett has made a version of their VNT-17 (1749VB) as a stock replacement for the KP-39

This turbo can be run in a stock BEW, but it also allows more airflow and can handle more boost than the KP-39. 165 HP/270 ft/lbs are possible with this turbo and the right tune and supporting hardware.

Want more?

For several years the VNT-17 was the upgrade turbo of choice for may ALH owners seeking more power. 180+ HP and 350+ ft/lbs are not uncommon.

Installing this turbo is fairly simple. The only major difference between it and a VNT-15 is the compressor (cold side) exit. The VNT-17 has a clip fitting that requires a VW hose or an adapter.

Unfortunately the hose runs about $200, but it allows the VNT-17 to plug right into most A4s. 1999.5 A4s will also need a new lower intercooler pipe, or charge tube, to accommodate the clip fitting at the intercooler end of the hose.

As mentioned above, the VNT-17 is also available as a stock replacement on the BEW, and is plug-and-play on that car. The turbo for the BEW includes a “smart” actuator that provides boost feedback information to the ECU.

Still want more?

If you’ve made other mods to your TDI including air handling (intake and exhaust) intercooling, fueling (bigger nozzles or higher pressure injection pump), and tuning and want more than the turbos listed above can provide, there are more options.

And although the VNT-17 is a popular upgrade on ALH engined TDIs, some drivers have found it less responsive (more lag) than the stock turbo. One way to reduce the lag and increase airflow is to use a larger compressor from a bigger turbo. This is how the 1752, or VNT-17/22, came into existence.

It is a VNT-17 with a compressor housing from a VNT-20. Because the larger compressor is spooling up a smaller exhaust wheel, it is more responsive than the VNT-17. Because it is made of components from two different turbos, it’s called a hybrid. And although its ability to make more maximum power than a VNT-17 is questionable, it does provide maximum torque sooner (lower revs) than the VNT-17 does in most setups. Here’s a dyno of the 17/22 in an ALH with many other mods.

Suppliers have also achieved this result by modifying stock VNT-15 housings to accommodate 17/22 or 18/52 internals. These turbos are available for both ALH and BEW engines, the only difference usually being the actuator. The BEW will usually require intercooler piping modifications for the hybrid intercooler pipe connections to fit properly, depending on the housing used for the compressor.

What to choose?

In summary, bigger turbos can mean more power. But sometimes they can jeopardize driveability with increased lag. Or they cause your car to smoke as they spool up, or cause you to need a new clutch to handle the increased power.

Best way to choose a turbo is to first identify your goal for increased power. Keep in mind that many tuners can improve HP and torque by 30% with a chip alone. Maybe that’s enough and you can stick with a stock replacement. But if you want more, happy shopping.

Related Products

Garrett VNT-15 Turbo (A4-ALH)
Garrett VNT-17/22 Hybrid Turbo (A4-BEW)
Garrett VNT-17/22 Hybrid Turbo (A4-ALH)

• Twin tube hydraulic (Reds and Orange)
• Low pressure gas (Yellows and Coilovers)
• Frequency selective damping (FSDs)

Reds have been around the longest, and are twin tube hydraulic dampers that are adjustable outside the car. So you pick your adjustment setting and forget it. On full soft the Reds provide a ride slightly firmer than new stock dampers, and offer improved handling. They lack the harshness I find on gas-pressurized dampers like the Bilstein TCs and, to a lesser extent, the OE Boge/Sachs dampers.

Koni STR.T are its newest line, designed to offer Koni quality and a lifetime warranty in a lower priced damper. They are twin tube hydraulic, not adjustable, and set to provide more damping than Reds on full soft. They are designed to work with lowering springs, and provide enough rebound damping to work well in those applications.

Yellows are low pressure gas dampers that are adjustable when in the car. In MKIV VWs only the fronts are low pressure gas and the rears are hydraulic, and aren’t adjustable in the car. This is because the tops of the rear dampers aren’t accessible from inside the car, like they are in MKIII and earlier VWs. Yellows on full soft are significantly firmer than Reds on full soft, and on their firmest setting are quite firm. Both Reds and Yellows, like most street dampers, are adjustable only on rebound. Compression damping adjustment is only available on some upper end coilover setups.

Koni Coilovers are low pressure gas dampers and include springs that are significantly firmer than stock. There are three major advantages to coilovers over dampers and springs: height adjustment, the ability to corner balance the car, and the ability to run varying spring rates. A coilover setup on its tallest height setting will be a bit lower than a stock setup, and can be up to two inches lower than that, or even lower if you select shorter springs. Like Yellows, Koni’s coilover struts are adjustable inside the car, shocks adjustable outside the car.

Koni’s FSD dampers incorporate what they call Frequency Selective Damping in their struts, while the rear shocks are low pressure gas, and not adjustable. The FSD technology provides soft damping on high amplitude movement, such as potholes and expansion joints, and firm damping on low amplitude movement, such as cornering transitions. This provides a strut that rides well on bad roads and handles well when you want to drive aggressively. Koni offers FSDs as dampers alone, and as a suspension setup with matched Eibach sport springs that lower the car about 1.5 inches.

Those are the basic differences. Now I can provide some application thoughts, based on my own and others’ experience.

Koni Reds work best with stock springs and wheels. They are not a damper for someone who drives very aggressively. Having said that, my wagon with Reds on 3/4 firm and stock springs is very responsive, rolls little, and still has a reasonably compliant ride. Reds do not seem to work very well with a heavy wheel/tire setup or upgraded brakes, as they have some difficulty controlling the extra weight. And they can work with lowering springs if you set the adjustment at least halfway between soft and firm. I have Reds on my A3 with Neuspeed Sofsport springs, set at 3/4 firm, and they control the stiffer springs well and ride quite firm. I do have light 14″ wheels and tires on the car, which help.

I’ve had the best hands-on experience with STR.Ts. However, reports from JasonTDI and MrChill say that they are firmer than Reds, provide better rebound damping than Bilstein TCs, and ride better than TCs, because, I believe, they’re hydraulic versus gas pressurized. I think these should be a great setup on a New Beetle, which basically has firmer lowering springs from the factory. And they should also work well if you run big wheels or brakes, or have your car lowered.

Koni Yellows are a great compromise between ride and handling for those who drive aggressively or run their car on the track. I ran Yellows with the Shine Real Street setup on my Golf the summer before last and they worked very well. On full soft the car rode well when going to the track, and on 1/2 firm the handling tightened up dramatically. This is the setup that many of you saw three-wheeling around the “low speed” autocross course at the Montreal Fest. The Shine/Koni Yellow setup is my idea of an ideal aggressive road setup, and good for track days, although the springs really aren’t firm enough for serious track use.

That’s where Coilovers come in. Koni says that their coilovers can accommodate spring rates up to 700 lbs. For reference, most stock front TDI springs are around 150 lbs., and rears are about 120 lbs. I ran my Golf with 550F/350R springs last year until my accident, and the car handled much, much better than with the Shine setup. I was able to run the car significantly lower, and used camber plates to keep the geometry in line. Later last summer I switched the coilovers to IBW and ran with 700F/550R. Believe it or not the car wasn’t as punishing to ride in as you might think. And it cornered beautifully, totally flat. I put the stock Koni springs in the car at the end of the season (350F/190R) but couldn’t get the ride height up enough to make driving the car in snow worry free. But it rode and handled very well with those springs/dampers. I had the car corner balanced with both setups, and this does make a significant difference on the track, maybe not so noticeable on the street. I can say with some confidence that a Jetta Wagon wasn’t really made to be corner balanced. The fuel tank is in the wrong place. I guess it really isn’t intended as a track day tool, but tell that to the people I passed.

If you like a car that handles well and don’t want to sacrifice ride quality, the FSDs with stock springs are a great combination, and is really excellend if you add a Shine rear stabilizer bar. They really do work, and in about 40K of use I only found an occasional time where they would be caught off guard, such as a dip right after a bridge on the freeway. They seemed to be in soft mode for the expansion joints and the dip would catch the damper in soft mode, causing the car to bottom. This is very rare, however. I can only remember one place where I could repeat it, on 495 near the Ho5G. I even did a track day at Lime Rock in the wagon with them, and they did very well. They really are remarkable. They don’t work quite as well, IMO, with heavy wheels and brakes, or with a combination of heavy wheels and lowering springs. They don’t have quite enough overall damping for those setups. I read somewhere that the FSDs do the best job of overcoming what is a pretty primitive suspension setup on the MKIV cars. I’d agree with that. If you want your Jetta to ride and handle like a 3 series, FSDs will get you closer than anything else.

I warned you it would be a long answer. But to summarize:

• Lowest cost, firm damping: Orange
• Closest to OE ride, better handling: Red
• Firmer damping and adjustability, best able to handle big wheels and brakes: Yellows
• Firmest ride, most adjustment, great for the track: Coilovers
• Better than OE ride, excellent handling: FSDs.

Hope this doesn’t raise more questions than it answers. But if you have more, ask away.

Related Products

Full collection of Koni shocks, struts, and springs for TDI’s