I've got a 91 3.1L AT and It's had a high idle for a while now. By high I mean after warming up it redlines in park/neutral, if I put it in drive it drops from 5k-6k to around 3k. The only way I can even warm it up is putting it in drive with the ebrake on so it doesn't redline. The problem seems to be getting worse though that might just be because it's colder now than when I started so it's idling up on a cold start to warm up.

It has dual snorkel intake, the pacesetter headers, deleted A/C, deleted smog pump/emissions crap, and a high flow cat.

I have looked at all threads about this on here and most if not all of them end in a dead end and aren't ever resolved, they all say vacuum leak or IAC/TPS.

I had tried listening for it, spraying starter fluid, and blowing smoke into the brake booster hose with the intake capped off, I also looked over all the vacuum lines I screwed with for the emissions delete and none of them are leaking. (I could not find any evidence of a leak)
Changing the IAC and TPS (with the battery reset).
Changing the O2 sensor for a 3 wire sensor off a blazer. (It didn't do anything so I reverted back to the stock 1 wire)
Resetting the TV cable to factory specs.
Checking that the gas pedal and throttle blade have full range of motion and aren't hung up.

So that's where I'm at, the headers were the last mod to be installed, after the installation nothing was wrong and sadly I do not remember what change initially caused this as it started a year or two ago and I gave up and let it sit. The CEL is out so I'm going to go out and replace the bulb to see if it's throwing any codes so I'll update this hopefully later today with any codes.

 

Try a different tachometer...

 

D

 

Do you mean that it might just look like the rpms are bad because the tach is broken because I can very clearly hear that it is not idling at normal rpms...

 

Yes, that's exactly what he means, if it were truly turning 5 or 6 thousand RPMs, I'm not even sure the transmission would allow itself to go into gear at that astronomical engine speed, but if it did, you'd do a mile long burnout

Your tachometer has obviously failed, as is a VERY well known & documented failure of these. As TL so rightly said, get a real (read=accurate) tach on it and see what it's actually running at. Sure it's possible the idle may be a bit high, but there is no way in Hell it's 5 or 6K RPM too high

 

Ok can't hurt to try, I'll go pick up an after market tach and see what it reads.

 

For the record, 6,600 is the highest reading I’ve ever seen for my car, and it sounded like a trailer park V12 Lamborghini Definitely check the tachometer and its connection to the dizzy.

 

Yeah it was the tach, I got the aftermarket one setup and it's showing normal. Oops lol.

 

The factory tach is an easy fix. There is a sticky at the top of the electrical forum I think