Thought problems were fixed but.....

[maynard]

O.K. I have a 91 Talon TSI. Ever since I bought the car a couple of months ago I've had idle problems. I've been using this forum and the VAFQ practically every day trying to get things fixed. My problems consisted of really high idle when cold and the idle would surge when it got warm. Here's what I've done so far. The really high idle problem consisted of the throttle cable being too tight so I fixed that. Had some vacuum leaks so I fixed all those and i blocked off the egr valve. Did a BISS adjustment and Still had idle surge. Tested my O2 sensor thought everything checked out good but I wasn't to sure about it because the idle was not real steady. Tested my ISC, it's crap, and i tested the TPS for the hell of it and I discovered the ISC and TPS were junk so I bought some used replacements. I double checked these according to everything I've read on here and my haynes manual and they're good. When I installed these I took off the throttle body, cleaned it up real good, got rid of all the gunk caked in it, and replaced the gaskets. Re-installed everything, did a BISS adjustment, now she's running good and idle is about 900 and staying steady. Great !!! Problems solved right.... NO. Now if I drive the car when it hasn't completely warmed up it will still surge. What I mean by that is I'm tooling along through town, come to a stop light, push in the clutch the idle will jump up to 1500 drop to 800, go back up, then down, it does this about 3 times then levels out about 900 and stays there. This is with the temp gauge around a quarter of the way up. Now if she's at full operating temp. it's fine. No surging, no high idle, nothing, car runs normal. I decided today to go back to the O2 sensor and check it out because I noticed that it seems to be running rich. I tested the sensor terminals with engine cold got an ohm reading of 13 between terminals 3 and 4. According to Haynes it should be approximately 12 at 68 degrees so that checks out. I then let it warm up to full temp and tested the sensor voltage. At idle it was reading .4 volts which according to Haynes is good, revved it up a little and it climbed to 1 volt and slowly came back down to .4 while at idle. I revved it way up and the voltage went from .4 to 1 then way up to like 1.76 volts. and slowly, and I mean slowly came back to .4 volts. Now my Haynes manual does not say anything about getting a reading above 1 volt. All it says is .4 volts at idle and as speed is increased it should read between .5 to 1 volt. So now I'm stumped and frustrated. Like I said earlier it seems like it's running rich because the exhaust stinks like it's getting to much fuel, burns the eyes too. That's what leads me to believe it's the O2 sensor causing my problem but I don't know for sure. I don't have datalogger yet because I'm a poor bastard. I know that would help me alot but I'm doing what I can without one. Again, when the car is fully warmed up I don't have any problems only when it's cold. 02 sensor bad or is it something else ? I'm all out of ideas. If you guys can help me out or point me in the right direction I would greatly appreciate it. I hope I don't get banned for asking another question about idle surge.

 

[97GS-TSpyder]

my car did that. thought it was normal. :shrug:

 

[AWDPetmitsu]

Just speculating, but maybe your coolant temp sensor is faulty?

 

[maynard]

Just speculating, but maybe your coolant temp sensor is faulty?

What makes you think it's the temp sensor ? I'm not being a jerk, I'm just curious

 

[AWDPetmitsu]

I'm just speculating, but since it's one of the inputs the ECU reads to adjust the air/fuel mixture and you say the problem isn't present when it's fully warm, maybe the sensor is flaky.

 

[maynard]

I'm just speculating, but since it's one of the inputs the ECU reads to adjust the air/fuel mixture and you say the problem isn't present when it's fully warm, maybe the sensor is flaky.

O.K. I decided to check out my coolant sensor and I actually discovered a problem. Well, actually I caused a problem. I checked the resistance on the sensor cold and according to Haynes it checked out. Next I let it warm up to full temp and decided to check it again but when I unplugged it the plug broke off from the wires. Anyway I rewired it, unhooked the battery to clear any codes this might have caused, and checked the resistance with the car at full temp and it checks out. Maybe because the wiring was rotton it was screwing up the signal to the ECM. I'm going to drive it and find out if I still have the idle problem.