1991, 305 with 175k miles. Have noticed this problem occurs irregularly. I cant recall any exactly when this started (not around any particular engine component change).

When it occurs, its usually never at first start in the morning, but later in the day when running errands.

Engine revs up to 2000 for a sec..then comes back down to a grand or so for a bit and then finally settling back into the 700 rpm range. Usually on cold starts, it revs to 1000/1100 for 30 sec before returning to 700 rpm.

I've noticed though that in the 3 years I've owned this car, that it takes a while to 'warm up' (i.e on cold starts it always revs to above a grand for at least 1 mintue before idling at 700-750 rpm.

Any thoughts/opinions?

 

Maybe you've just got some leaky fuel injectors that are leaking a little fuel down in the cylinders when you park it and when you jump back in and fire it up, it cranks for a second until it burns all that extra fuel which kicks the revs up. I dont know, just a thought.
As far as the high rpms on cold starts, thats normal. It's basically fuel injection's version of the choke on a carburetor. Rev it once when it's idling high, and within say 15 seconds or so it should come back down to a normal base idle. The high idle is just to get the engine to warm up so the computer can kick in emissions systems, etc. sooner.

 

Let's see....

A TPI, starting cold, idling high, then slowly dropping RPM as the ECM gets increasing coolant temperature data from the CTS. Sounds completely normal to me.

As for the RPM being at 2,000, you need to verify that with a handheld tachometer. It is very common for factory tachs to read higher and higher as they get older. The actual RPM may only be 1,500 or so, which would be completely normal for a stock TPI.

 

Yeah..I know..sounds dumb. Just wanting to be sure I'm not the only one taking 2 minutes to warm up. Sounds insignificant, but I hate my friends having to wait for the "bitchin camaro" to idle down.

As far as how high the revs go, I see your point. I guess I should say that although not exactly 2000, I can hear that its reving alot higher than usual. Like I said, not always.

My main concern was that a sensor was fouled. I've been obsessive about any little quirk lately because I am forced this year to take some 4 and 5 hour road trips and I don't want any 'surprises' along the way.

Thanks for the reassurance.

 

its happened to me quite a few times too. i remember as soon as i got it back form my mehanic one time it revved like that after cold start ups for weeks, then finally went back to normal. sometimes (mainly when its cold) it will do it to me again, in fact it did it the other day, so i dont worry about it.

but i was damn pissed when i got it back from my mechanic and it was revving like a bat outta hell when it first started!!!

 

I get the same thing. 11-1200 when first started cold, then if I take only a short drive, shut it off, then start up again a few minutes later it rev's up to 1800 then back to idle. Then normal again later.

 

Hey man,

I recently got my car back (like in December) from the Dealership and it started idling high! I was like :O it's never done that before! I'm going on a two hour drive tomorrow morning and was hoping my "old faithful" wasn't going to leave me high and drive on the road. If other people have had this problem and the car is still working fine then I'll take if for granted that my car is working in it's normal means as well. Also, If it's still idling high during the spring and summer I'll talk to the dealership about and find out what needs to be replaced.

 

How high are we talking here?

Check the idle stop screw behind the throttle plate first to make sure it hasn't been cranked out for any reason. Also make sure the throttle blade is closing completely and not hanging up on either any of the cables/springs, or due to any gunk/deposits on the blade edge. Then with the car off, disconnect the IAC valve, and start it. No more high idle? Check TPS voltage at KOEO with a digital voltmeter...there should be instructions on this site as to which wire to probe and what the voltage spec should be. If it's out of spec, loosen the retaining bolts and see if it's adjustable by attempting to swivel the plastic sensor inside its housing. It should rotate a certain amount if this is the case, just bring it as close as possible to the middle of the specifications. Also perform a sweep test--careful watch the voltage while SLOWLY opening the throttle, KOEO---the voltage should rise steadily up to the peak specification for wide-open. If it fluctuates at any point in the sweep, or voltage stops increasing at any point, the sensor is defective.

If the high idle remains, and the throttleblade is in a normal position, and TPS voltage is in spec, you've got two likely possibilities --a vacuum leak, or a stuck IAC valve. There are probably two screws holding the valve and motor assembly in. With the ignition OFF, disconnect it, and remove the assembly. Spray it down with some carburetor cleaner thoroughly--avoid pushing and prodding on it hard because you could either send that spring flying, or damage the stepper motor. Check for vacuum leaks by listening for any unusual hissing noise under the hood. Also, being careful not to SATURATE any areas, mist throttlebody cleaner all along the intake manifold and vacuum lines with the motor idling. If there's a leak, it will pull in the cleaner and cause the engine to rev up.

It's got to be either stuck/cracked throttleblade, vacuum leak, out-of-spec TPS voltage, or stuck IAC valve. Or if they made any significant increase to the base ignition timing...but more than likely the high idle would be accompanied by pinging and increase in engine temp.

 

Sorry I just stumbled upon this board and saw that you replied to me. Well, that would definitely explain my high engine temp. I just took out my thermostat because the temperature would rise to just under redline with that on. I'll be home this weekend and will start checking all of these things systematically. Much thanks man.

 

No problem...my god are you late with this reply haha. I havent been on this board in forever. Since youre running hot ALSO, this very well may be a timing issue...would explain both, but a high idle would explain running hot AT IDLE but not during driving since youre off idle all of the time. If it idles high and runs hot during driving, definitely check your ignition timing, I'm betting it's too high.

Man I havent been on this board in a LONG time!!