I've been trying to sort out the idle on my 89 TPI 5.0 for a while now, and it's starting to p!ss me off.

The car usually idles about 1200 (60% of the time), but frequently decides to run up to 2500-3200 or even more. This morning it idled at about 3000 during my entire 30 minute work commute. Once in a while it'll decide to slow to 900 or so, but not very often. It's smooth and steady, just unpredicatble and ridiculously fast too much of the time. It started this when I changed injectors and chip.

I drive this car to work every day. Can someone help me out?

This is what I've done so far:
TPS
IACV
Bosch 3s
TPIChips chip
O2 sensor
Set base idle a few times
Looked for and fixed vacuum leaks

Sometimes it'll be idleing fast then slowly come down on it's own over about 10 seconds, but usually it'll stay wherever it is when you first start the car, which can be anywhere.

 

you sure you still dont have a vacume leak ????
try spraying intake when runnin with carb clean or anthing flamable.
and see if idle picks up or pull off a vacume line and and using compressed air pressureize the intake and listin for a leak.

 

probly a bad ecm,next time it races bang on the dash(the front not the top) on the pass. side near the rs/z28 emblem the ecm is behind there.smack the dash if it changes the idle its the ecm. if it was a vacum leak it would always race or stall not randomly.

 

my suggestion would be, have you tried logging data to see what the IAC is, what the commanded idle rpm is, what vacuum the ECM thinks it's seeing, etc.

but that has 2 big presumptions: that you have a laptop, and that you have the ALDL cable to hook up to said laptop.

otherwise, some major data-collecting hurdles to overcome. not sure how i'd troubleshoot some of these high-tech symptoms without these "tools".

sorry, not much help.

 

look at the throttle plate inside the throttle body.. they should be closed.. could be the linkage for accelerator pedal. vac leak would be always there. it could be the brake booster leaking also. the engine needs air to race.. somewhere air is getting in.

 

A guy can never be sure that there are no vacuum leaks, but I've gone over it pretty good and can't imagine that I've overlooked anything significant.

There's no binding in the cable/linkage. I've pulled over and gotten under the hood and checked while the car was actually in the act of being a dumb@ss, not to mention kicking the gas pedal about a thousand times thinking something might be binding. Never has any effect.

Next chance I get, I'll bang on the dash. Who knows...

I have a laptop, but no cable. Where to I get one, and what do I do then?

By the way, the car got even with me the afternoon after starting this thread. Fuel pump went out in the middle of a busy intersection in Fort Worth rush hour traffic. P.O.S. I had to get a neighbor to tow the car home with his Taurus station wagon. Most of my stodgy neighbors, who think I'm flipped anyway for keeping such an old car, and working on it all the time, just happened to be outside tending their daffodils and saw me come creaking in. Mostly, they just shook their heads. The smokin hot 22 yr old home wrecker/gold digger next door kept walking by yesterday afternoon asking if I'm "havin' fun yet", as I screamed profanities every time I busted a knuckle or took another face full of rust. Getting the tank out of these cars SUCKS when your 50 and working alone.

 

forget the brake booster it would be constant and hard to stop the car.throttle cable you would feel the pedal stay down,vacum leak would be constant.if it happens randomly on and off and above the fast idle of 1200-1500.the ecm is probably trashed. lower the ecm down get the car to race and when it does give it the tap test.i have seen it before.the ecm will command the iac to open way to far.

 

Sooo is the ECM the chip, or the thing the chip goes into? It's possible I didn't disconnect my battery when I changed the chip...in fact I'm pretty sure I forgot to do that. Maybe part of the problem? Do I just dig around in the salvage yard for another or what?

 

you should have disconnected the battery before you changed the prom. the ecm is silver and the prom goes inside it. a new ecm should be under a 100 new. junk yard may have one for about half that.

 

50 years old and finally made a mistake! I feel so 'regular'.

For that money, i'll give it a shot. Any idea what the chances are of getting a good one or bad one when buying salvage?

 

its not the ecm/prom.
2 possibilites that cleared my SAME problem.
The vacuum that switches from vent/floor/defrost
or, just ohm test your injectors see if 1 is bad. <----was my problem, 1 bad injector

 

Put the stock injectors and chip back in and see if the problem goes away, if so you probably have a defective chip/injector or more tuning issues

 

a bad injector will cause a skip or low idle, also you can pull off the hose for the vacuum to the heat and the rpms wont rise more than 50-100 rpm.hes got an intermittent idle of 2500 rpm!!!!!you can pull off all the vacuum hoses and not get 2500 rpm!!!!! so think about your ideas before you post.not to sound like i know it all but i do this for a living.these ecms have a pretty high failure rate and most of the cars that use them are probably out of the yards.witout actually seeing the car id say try a new ecm and if you have the original prom put that back too.till you get this nailed down.

 

Here's the ECM I got. Not to say it will fix all your problems but it's cheap enough to take it out of the equation... Good luck!!

http://shop.advanceautoparts.com/Pro...pe=248&PTSet=A

 

If you have a high idle you need to check your Disconnect your throttle linkage to ensure it isn't binding, Then unplug each vacuum line 1 at a time and plug them. If your engine is still at an unusual idle, Short out your A-B pins on your ALDL then turn your key on for roughly 1 minute to put your car in diagnostics mode. Unplug your IAC and then start your car. This will also put your IAC at a 0 count. and it should idle at approx 400-450 rpm. If you are still getting a high idle and your IAC checks out ok then get out the WD-40 or starting fluid and spray your intake manifold along the front, sides and rear to ensure you intake manifold gaskets aren't leaking. If all else check your ECU & Prom. Always start with the engine and work to the ECU

 

he already did the basics like check for vacuum leaks,check the throttle cable and reset the tps and what not.

 

90% of the problems that I encounter with these are what I have stated and I also work on alot of these and I have encountered 2 with ECM failures because of someone who didn't know how to repin an ecm and the other because if was drowned with water. He has a TPICHIP which would be more likely to have problems than the ecm to fail. He stated that his problem also started with a TPICHIP... I would check that 1st.

 

Yep, I've done all the obvious stuff and can't account for the condition. I've got a buddy who probably has a spare ecm I could experiment with. I'll email TPIchips and see what he has to say as well.

The IAC is only a few months old, but an autozone item. It could be a problem I suppose.

 

i had the same problem w/ my car. did all the normal checks and the tps was out of range. reset it it ran fine for a few days and started doing it again. rechecked it was out of range again, replaced it no more problems.

 

I check the tps voltage just about everytime I raise the hood. It's always on the money or pretty darn close. I'll try to round up an ecm this weekend and maybe we can put this thing to bed.

 

o, my bad, i didnt notice u said it started when u changed injectors... you really wanna know wut i think the problem is, and im almost 100percent sure? Manifold leak. take that puppy back off and reseal it.

 

Don't you mean that you check the OHM reading on the TPS.. Should be around .45 at idle and over 5 at WOT.

 

Just a thought, what is the flow rate on your new injectors? A stock 305 uses 19lb per hr.And your chip was probably written for 19lb, but if your injectors are flowing more, say 24lb, that could cause a world of problems.

 

Check your idle screw first and see if you can bring it back down with that. If that doesn't work, check your IAC. The plunger may be sticking. If thats the case, it will have to be replaced.

 

.54V at idle, isn't it?

 

Yes, Idealy most cars will want .54 at idle. Basically even with tuning, you give the car what it wants. My point was to use an OHM meter not a volt meter. Thanks for getting me straight though.

 

The injector constant has been adjusted for 22lb injectors. I don't think it's a rich/lean condition, as I think the o2 sensor would throw a code if it was too far out.

I've shut the IAC and set minimum idle several times. Slows to a nice tick, then gets weird again when I plug up the IAC. Last summer I left the IAC closed and disconnected for a few months. Got tired of holding my foot on the gas until the motor warmed up.

The IAC has been replaced, so I assume its good.

I probably should just get the datalogging software and get serious about this.

 

start with your last action, the injectors and prom, replace your injectors and prom with stock again, also in my experience, injector replacement LOVES to cause vacuum leaks, you already checked that, so we wont bother there. i think it is linked to thew prom and injectors.

 

Too late. Multecs went in the dumpster. Four ohmed bad anyway. I could still try the original chip, it would just run a bit rich, but might give some good info.

 

I am having almost the same problem here. Sometimes it will race and when I turn it off and restart the idles go up and slow back down where they are supposed to be.

Also, if I run it at night and come back in an hour or so, I have to crank the hell out of it to get it to restart. It will eventually restart and puff out some smoke.

Are you having any other weird issues with your car? Maybe we can pinpoint it with more information.

Just out of curiosity, what brand are the TPS and 02 sensor?

I had a lot of problems with GP Sorensen compatibility and my ECM.

I have also heard of people fixing this issue because of the distributor housing being worn.

Have you pulled the throttle body off and cleaned it thoroughly?

 

ever think about the MAF? will cause the same problem and they are notorious for going bad on F-bodies.

 

You know what, I have another TPI camaro with a good idle and maf, I am going to swap them over and see if it makes a difference.

 

still say pull the manifold off and make sure everything is sealed.........

 

im have the same problem did you ever solve this

 

Instead of pulling off the intake you can spray the intake with WD-40 or Ether with the car running. The idle will race or drop if there is a vacuum leak.

 

I FIGURED IT OUT!!!!!!

ok, i've been fighting this for about 4 years now. I have Gen 7 and figured i just don't know how to program it. i tried everything you guys have mentioned and changed TIMING, FUEL, IDLE MODES, EVERYTHING!!!!

HERE IT IS>>>>>>>

2 things: My idle speed was set too high and the IAC couldn't compensate for the air getting past the blades. the IAC would read 0 and it was at 1700rpm. I turned down the IDLE SCREW and it idled at 860 (where it is programed to and an rpm it has NEVER seen before!)

I drove the vehicle and after about 10 minutes it started to creep up again to about 1500rpm, then sometimes it would be at 860.

although i cleaned the crap out of it when i put my stealthram on I found more CARBON build up on the top of the throttle body that the plates were getting stuck on and causing the plates not to close all the way. about 1/16 to 1/8 away from the idle screw. cleaned this up and it's been PERFECT for teh first time in 4 years!

I did read a little something about the BUSHINGS for the throttle plate bar wearing out and causing the blades to get cocked and not close all the way but luckily mine was just a tiny piece of CARBON!!!

good luck guys