Idle Issue 89 GT

[89GT]

I picked my 89gt up sunday and found out that the TPS is unplugged. Let me start off that it had a surging idle it would go from almost dying to 1000rpm and sometimes it would die. I pulled the intake apart, cleaned the MAF and found the TB to be very dirty, cleaned that, and plugged the TPS in and took it for a drive. Ran excellent until I got in it the next day. Ran good until 5 min of running and the idle shoots to 2000rpm and stays there. I Pulled over and disconnected the TPS and the idle is perfect. Now, I was thinking mayb the computer needs to be reset because it has parameters set from running without a TPS signal for so long, and then plugging it back in confused the ecm... does this sound feasible? I haven't tried yet, but I plan on doing the idle re-learn procedure in the near future. TPS voltage at idle is .65, What do you think?

[SloSVO]

the tps voltage is a bit on the low side.. I shoot for .95 KOEO.. next time its stuck like that look at the Tp voltage.. you may have a shorted sensor..

[ChuckD]

If you wanna come by I can give you a hand crossroads are Cactus and El Mirage.

[89GT]

the tps voltage is a bit on the low side.. I shoot for .95 KOEO.. next time its stuck like that look at the Tp voltage.. you may have a shorted sensor..

I figured it was low. Articles say to shoot for .98-.99 so I will have to hollow the holes a bit more to achieve that. I got the car with the TPS disconnected, it runs good with it off, but smells rich. The IAC seems to be functioning properly. I will have a look at it this weekend more in depth. Thanks for the offer SloSVO, if I can't fix it I will take you up on the offer.

[1tuff68]

As long as TPS voltage is between .5 and 1v you are fine. The computer takes the baseline tps voltage reading and then subtracts the baseline value out of the current reading to determine how far the throttle is open. That's why TPS sensors aren't adjustable (you have to slot the holes to adjust). If it's not reading in the acceptable range without modifying it, then get a new one.

This is the best trouble shooting guide I've seen for surging idle:
http://www.stangnet.com/mustang-forums/698148-help-me-create-surging-idle-checklist.html

[89GT]

Thank you!

[1tuff68]

Let us know how it turns out

[89GT]

Let us know how it turns out

Ok, I disconnected the battery, connected the TPS back up, and started it up, ran good for maybe 5 min, then rpms creeped to 2000rpm... I can disconnect the TPS and it runs fine. I think I am going to try a new TPS.

Joe

[89GT]

Installed a new TPS and it has .97 volts now. But when I connect the IAC back up it starts running really erratic, it surges alot and stalls. I think the next step is going to be the IAC itself.

[89GT]

Did the idle reset and it still wants to climb rpms. when you blip the throttle it seems like it gets stuck then over compensates. Tomorrow I am going to replace the IAC and see what happens. I unplugged the MAF and it died so I think the MAF is working. Only leaves one thing... the IAC.. Will update tomorrow.

[89GT]

I cleaned the IAC too, looked like fresh oil on it, Maybe the engine has excessive blowby... It ran good for 2 min of driving then ran like crap.. Runs great with the IAC disconnected..

[89GT]

OK, this is an old thread, but now I have considered selling my stang. TPS voltage is correct, now I have bypassed wires in the "salt and pepper shaker" that send signals to the pcm from the tps, I found a bad connection in there (you can wiggle the connections behind the intake and it would lose connection). So, connections are good, now I have bypassed the IAC wire in the middle of the white connector (B/W wire). But it will run fine, then stick at 1500 rpm.... I need opinions. Do you guys think the IAC is sticking? It is sluggish when shifting (rpms stick). Thanks a ton in advance. I must add, the exhaust seems very rich and is almost unbearable to drive. And it does not have the power it should (tons of low end, but loses mid-upper hp). also has new 02 sensors.