Idle and TPS question.

[1LE]

First off, I'm *very* familiar with the BISS backing out issue, and mine is actually RTVd into place due to that.

So, no, it's not backing out, but my idle is creeping high anyways. Since it's been doing so, I've also noticed that my TPS no longer reads 0% at idle. it's bouncing around between 0.5 and 1.5% on my AFC during normal driving, and the amount that the idle is high seems to correlate with how high the TPS % is... So, that's my leading candidate...

I've verified that there are no cable issues, the throttle snaps solidly to the fully closed position. There have been no changes to the throttle area, nor the BISS.

Questions are:

- What TPS % do you all see at "idle", and on what device? My thought is that when the idle position is achieved, the ECU should go to 0% (even if it thinks otherwise for some reason). Side note, one ECU/tuning guide I found claims that I should see 10% at idle and 100% at the ECU and 0% idle and 100% WOT on the AFC. I did a quick comparison of ECU vs. AFC in the driveway and found that "idle" currently is 0.5-1.5% on both the ECU and AFC (exactly mirroring each other) and that WOT is 90% on the ECU and 100% on the AFC...

- Would a vacuum leak (or post MAF air leak) somewhere confuse the ECU into not seeing true idle?

- I'm thinking I'd like to pull the TPS connector to do the resistance checks, but I can't figure out how the clip-on connector works. How do I remove that connector without breaking it?

 

[Dhan]

The TPS is a critical component for the ECU and tells it whether you're cruising, WOT, or at idle. This is especially true on our cars that lack a large number of inputs for the ECU to use. If the TPS is off and the throttle plate is seen as open 2%, but your speed is 0mph, the ECU is not using the proper table to idle the car.

At idle and 0% throttle, the TPS should read 0.63V. If you have DSMlink, you can compensate for a slightly misaligned TPS. If you do not have Link, it must be done with a multimeter and turned by hand.

It sounds like you may have a mechanical issue that needs attention. If your throttle cable is stretched or you still have the old cruise control, it may be causing a hang up. The butterfly valve's spring may also be "sticky".
You mention that you have the BISS RTV'd, which IMO is just a band-aid. If you needed to do that, then your TB is probably in need of a rebuild (as a bonus, you'll fix any boost leaks in the TB).

I'm talking from some experience. I had a 1g that had a problem with the TPS. I switched out the TPS with a working unit, replaced the throttle cable, and WD-40'd everything. Nothing helped. So I ordered a TB rebuild kit and finished reinstalling the rebuilt TB last night. That fixed my problem. TPS functions as it should 100% of the time now.

And finally, to unplug the TPS harness: there is a tiny metal clip that needs to be pulled off first. I use a razor blade and a small pair of pliers to slowly wiggle it off. Be careful it doesn't go flying!
Once that little clip is removed, the plug should slip off.

 

[luv2rallye]

Here's some closeups of the TPS connector. It and the VSS connector clip (same) gave me so much trouble I thought I'd take some pics to help others. Don't lose that clip - it wants to go flying when you remove it. I used tiny jewelers screwdrivers and pliers. When you reinstall it it's easyest if you put the clip on last - and it will be a challange - again don't loose it. Notice the middle of that clip must go under the tab when correct.

 

[DSM1G90]

..and the same kind of clips for the harness connections to the injectors. Don't lose them and put them on last.

 

[1LE]

Excellent, thanks! Now I just need the free time to have at it!

 

[serviceguy]

You don't want to break those two little tabs that hold the metal clip in place. What I do is to slip a small flat screwdriver in between the two clips and push the clip down before pulling it out preventing it from springin away with my fingertip.

 

[lasershark]

so off topic vaguely i know the 2g has a 4 pin tps and the 1g has a 3 pin, but by change would a 2g tps work on a 1g?

thanks

 

[serviceguy]

The 2g will work on a 1g but not the other way aroung since the 2g incorporates the idle position switch that in a 1g is on the other side of the throttle body. That is what the 4th pin is for and it would not be used with a 1 g harness.

 

[1LE]

You don't want to break those two little tabs that hold the metal clip in place. What I do is to slip a small flat screwdriver in between the two clips and push the clip down before pulling it out preventing it from springin away with my fingertip.

I ended up having to get a small punch tool and press the the spring on the "bottom"/where it sticks out a little. That then gave me enough room to slip a very slim screwdriver into the newly created gap on the "top" and pry the clip loose. Not too bad now that I've done it, but it was truly a head-scratcher before!

...and the results.

- Idle switch activates per specification.
- Static resistance is solidly within spec, showing 4.5kohm, with the spec range being 3.5-6.5kohm.
- Dynamic resistance runs from around 1.5kohm at idle up to 5.8kohm at WOT. I do NOT have specifications for this. The book just says to verify that it moves smoothly with throttle position changes (which it does). Does anyone know what it should be? If not, what do you see on your car?

End result. I have no clue why my car thinks I'm pressing on the gas lightly at idle. Everything checks out, unless that dynamic resistance turns out to be out of range. At some point (next major maintenance window most likely) I'll be proceeding with the TB rebuild as suggested.

 

[serviceguy]

Did you try to loosen the TPS screws and rotate it slowly until the idle switch is engaged? Since it needs to be on only when your foot is off the pedal the best way to adjust it would be start with the idle switch on, rotate slowly until it goes off and the back it up just enough to make it go on again.

 

[1LE]

Did you try to loosen the TPS screws and rotate it slowly until the idle switch is engaged? Since it needs to be on only when your foot is off the pedal the best way to adjust it would be start with the idle switch on, rotate slowly until it goes off and the back it up just enough to make it go on again.

I made no changes to the TPS screws in regards to the idle switch as it engaged exactly per specification in the manual. I clipped onto the terminals and ran it back and forth a number of times, it's dead on perfect already.

 

[serviceguy]

Maybe the wire is broken?

 

[1LE]

Maybe the wire is broken?

It *appears* to be fine on the TPS end, but that's certainly a possibility. I'll have to try and locate where it comes out on the ECU side and test it. Not looking forward to that, getting at the ECU is not a pleasant experience, there's a ton of balled up wiring all around it that I hate disturbing!

 

[steve]

- What TPS % do you all see at "idle", and on what device? My thought is that when the idle position is achieved, the ECU should go to 0% (even if it thinks otherwise for some reason). Side note, one ECU/tuning guide I found claims that I should see 10% at idle and 100% at the ECU and 0% idle and 100% WOT on the AFC. I did a quick comparison of ECU vs. AFC in the driveway and found that "idle" currently is 0.5-1.5% on both the ECU and AFC (exactly mirroring each other) and that WOT is 90% on the ECU and 100% on the AFC.

The SAFC Throttle position is scaled, it shows it's output as a % of the low and high voltages that it's seen in use. If you look at the sensor check screen you can read the actual voltage currently output.

The 2G ECU software and OBD II protocol also displays a scaled value.

Factory 1G software and logging display a absolute percentage based on 0-5v range. So a 1G at idle will display 10% is adjusted to factory spec.

The output voltage of a 2G TPS at idle isn't specified exactly. The FSM says something like 0.4 to 1.0v. it depends on where your IPS switches and not on the voltage.

SInce both the AFC and the ECU are saying that the voltage is varying I'd look to see if any other voltages are also changing at the same time. Perhaps it's a bad ground?

 

[1LE]

Found one problem already. Fast idle coolant hose was leaking. I'd been losing small amounts of coolant for a little while, but could never find a source. Hose burst at work the other day, it was in horrible shape, probably was the source of my leak. After replacing the hose the first time I ran the car it obviously noted a change as it started doing the "rev way too high, hit the rpm cutoff, drop, rev too high, drop" thing. Haven't had a chance to drive the car enough to get the computer happy again.

 

[1LE]

Happily idling at 750 rpms again.

I'd failed to realize that replacing some old rusted piping could make such a significant change in vacuum and was misled by the odd TPS indications I was getting...

Does not appear to have any vacuum leaks, yet it took 1-7/8 turns (tighter) of the BISS to get into a range where the ISC is effective. I don't have the right scantool to center the ISC, so I ran the BISS down (at standard temperature) to the low 700's, then let the computer adjust. I then allowed the car to heatsoak and did multiple hot starts in between periods of driving. There's sufficient ISC headroom (on the loose side) for it to find idle fine under all conditions tested (and the drop rate was good, didn't drop too low nor bounce up too early). However, that only solidly tests one end of the range, I'll have to wait for Winter to confirm the other end of the ISC range.

BISS RTVd back down for now. TB overhaul will happen at next major service.

 

[Ludachris]

Happily idling at 750 rpms again.

I'd failed to realize that replacing some old rusted piping could make such a significant change in vacuum and was misled by the odd TPS indications I was getting...

Does not appear to have any vacuum leaks, yet it took 1-7/8 turns (tighter) of the BISS to get into a range where the ISC is effective. I don't have the right scantool to center the ISC, so I ran the BISS down (at standard temperature) to the low 700's, then let the computer adjust. I then allowed the car to heatsoak and did multiple hot starts in between periods of driving. There's sufficient ISC headroom (on the loose side) for it to find idle fine under all conditions tested (and the drop rate was good, didn't drop too low nor bounce up too early). However, that only solidly tests one end of the range, I'll have to wait for Winter to confirm the other end of the ISC range.

BISS RTVd back down for now. TB overhaul will happen at next major service.

What piping did you replace? Water pipe?

I'm pulling my hair out trying to figure out my idle problem on my 97 TSi. I've eliminated the FIAV completely, but plan to put it back on. I've fixed all the boost leaks I can hear. I've changed out the throttle body to a low mileage rebuilt 1G n/t 63mm option that I had used for a little while on the 1g GSX track car with no issues. I've checked that the TPS reads .63 in Link at 0% throttle. But every time the car gets fully warm after a drive, the idle will climb and hover around 1500 rpm, sometimes up to 2k. It seems like it's related to temp. Brian's bringing another TPS to the Shootout this weekend so I can try it out. The only things left to try that I can think of are replacing the EGR valve and front O2 sensor. I don't have the rear O2 sensor hooked up since the catback I'm using doesn't have a provision for it.

 

[1LE]

What piping did you replace? Water pipe?

I'm pulling my hair out trying to figure out my idle problem on my 97 TSi. I've eliminated the FIAV completely, but plan to put it back on. I've fixed all the boost leaks I can hear. I've changed out the throttle body to a low mileage rebuilt 1G n/t 63mm option that I had used for a little while on the 1g GSX track car with no issues. I've checked that the TPS reads .63 in Link at 0% throttle. But every time the car gets fully warm after a drive, the idle will climb and hover around 1500 rpm, sometimes up to 2k. It seems like it's related to temp. Brian's bringing another TPS to the Shootout this weekend so I can try it out. The only things left to try that I can think of are replacing the EGR valve and front O2 sensor. I don't have the rear O2 sensor hooked up since the catback I'm using doesn't have a provision for it.

The intake and LICP were both rusted horribly. Replaced the intake, UICP, LICP, and SMIC... I'd swapped SMICs before with no change, just never ocurred to me that it might be the cause!

I doubt your problem is the EGR or front O2 sensor. I had the EGR fail once and I've gone through a number of front O2 sensors. Never had a rising steady idle. Not familiar with your TB, but if it's like mine there's 3 things on it that control the airflow (never mind the fuel trim/TPS stuff)! SAS, BISS, and ISC all have to be in appropriate ranges. Another thought, are you getting appropriate coolant temps coming back from the link? I had some wacky idle issues in the past due to bad coolant temp sensor...

 

[Ludachris]

The intake and LICP were both rusted horribly. Replaced the intake, UICP, LICP, and SMIC... I'd swapped SMICs before with no change, just never ocurred to me that it might be the cause!

I doubt your problem is the EGR or front O2 sensor. I had the EGR fail once and I've gone through a number of front O2 sensors. Never had a rising steady idle. Not familiar with your TB, but if it's like mine there's 3 things on it that control the airflow (never mind the fuel trim/TPS stuff)! SAS, BISS, and ISC all have to be in appropriate ranges. Another thought, are you getting appropriate coolant temps coming back from the link? I had some wacky idle issues in the past due to bad coolant temp sensor...

Forgot to mention I replaced the coolant temp sensor. In deleting the FIAV I also deleted the ISC. The BISS should be in range but I'll check again... I'll have to double search again on how to determine that it's in range.

 

[steve]

In deleting the FIAV I also deleted the ISC. The BISS should be in range but I'll check again... I'll have to double search again on how to determine that it's in range.

With both the ISC and FIAV gone the BISS is a static idle speed setting, no range, one setting.

 

[Ludachris]

With both the ISC and FIAV gone the BISS is a static idle speed setting, no range, one setting.

What's the setting for a 2g? On a 1g, I remember it being something easy like 2.25 turns out from fully seated.

 

[steve]

What's the setting for a 2g? On a 1g, I remember it being something easy like 2.25 turns out from fully seated.

What ever spot causes your engine to idle at the right speed? What have you got Link set for?

If that turns out to be around 2-3 turns out, cool. You've changed so much that it's not going to be like stock. Both the IAC and FIAV provide varying amounts of idle bypass air and now you have to make up for them missing.

 

[Ludachris]

What ever spot causes your engine to idle at the right speed? What have you got Link set for?

If that turns out to be around 2-3 turns out, cool. You've changed so much that it's not going to be like stock. Both the IAC and FIAV provide varying amounts of idle bypass air and now you have to make up for them missing.

I have link set to 850 RPM, and that's what it idles at for a little while before I do much driving. So should I adjust it when the RPM is stuck at one of the higher levels? Before I removed the FIAV and fixed the boost leaks I remember closing the BISS completely one time when the idle was stuck up at around 2k and it didn't do anything. I'll try it again though today when I get home, as the idle is usually pretty high by that time.

It seems there are about 3 levels depending on how hot it is outside and how much driving I've been doing. After a short drive in warmer weather it moves up to around 1100 and sits there for a little while. Then, after more driving it will jump up to around 1600 all the sudden and stay there. If it's really hot it will jump up to 2k and hover there while driving. At that point I turn on the A/C, which seems to drop it back down to about 1k with some erratic jumps every so often. There is no surging, just sticking at a certain RPM. The stock water temp gauge stays the same but I think the car runs a little hot, up around 215-220 when it's really warm out.

 

[Ludachris]

Just went for a drive on my lunch, drove to the store on city streets. When I got to the store the water temp was at 219. The RPM was at 1900, STFT was something like -18, the TPSVolts was .73, the front O2 stopped cycling and was stuck at .96. Not sure what else I should have looked at. I got out and tightened the BISS screw in all the way and it didn't change the idle at all. Turning it the other way didn't do anything either. By the time I got back to work the RPM was 2300.

 

[RocCitySlayer]

Can a 1g Tps be used in a 2g if the idle switch is simulated in dsmlink?