3100 High idle issues (1,500-3,000rpm)

[logikfive]

I purchased a '97 Lumina LTZ off eBay in early February with bad lower intake manifold gaskets. I replaced them, and ever since it has idled really high when cold (3,000rpm), and slightly lower when warmed up a little bit (1,500rpm). When you start it when it's cold, it'll start out at like 1,200rpm and creep to 3,000rpm. I never started the car when I bought it in fear of doing more damage (as it has 219,920 miles on it) so I cannot verify if it did it before the gaskets. It purrs like a kitten, but I cannot figure this thing out. Everything I do to try and slow the idle down makes absolutely no difference. Here is a list of things I've changed:

-TPS Sensor
-IAC Sensor
-MAP Sensor
-Temp. Sensor
-PVC Valve (rattled internally)
-Hooked up a vaccum gauge, was within specs. I even sprayed starting fluid around the LIM gaskets, and all the visible vaccum lines for added assurance.

I have run out of ideas. Is there any chance it could be EGR valve related? Oxygen sensor related? Perhaps even a bad computer? If I have it hooked to a code reader, will it show anything? It throws a SES code, but I'm 100% positive it is because it has a bad gas tank.

Also, the only way I could get the idle to drop down to somewhat normal was to plug the PVC valve (approx 1,200rpm which is still a little high, but better than 1,500-3,000) However, I'm sure it's not a good idea to plug that.

Any help on where to possibly look is appreciated. This newer crap really burns my bottoms.

[rx191]

yes the check engine light will tell you something, probley a idle code though, a bad gas tank will not set the light untill you drive the car a couple of times. check for vacuum leaks everywhere, 3000 is way too high the engine should never idel over1500. also check for a faulty oil cap, if it doesn't seal well you will the high idle, i work on cars for a living so i will try and help you my best with this problem. also the pcv valve is supposed to rattle when you shake it thats the valve inside of it.

[logikfive]

yes the check engine light will tell you something, probley a idle code though, a bad gas tank will not set the light untill you drive the car a couple of times. check for vacuum leaks everywhere, 3000 is way too high the engine should never idel over1500. also check for a faulty oil cap, if it doesn't seal well you will the high idle, i work on cars for a living so i will try and help you my best with this problem. also the pcv valve is supposed to rattle when you shake it thats the valve inside of it.

I've checked for vaccum leaks using starting fluid, I sprayed everywhere I could possibly spray and the idle did not change. I'll check the oil cap, that never crossed my mind. As far as the PCV valve, I should have stated it rattles like it's supposed to when you have it in your hand outside of the car, but when it is plugged in it chatters.

Edit: Checked the oil cap, no difference.

I appreciate your help as well as any other suggestions you may have!
Thanks.

[tractorman]

With an idle that high, you might not notice any difference with starting fluid even if you spray it in the leak. I think you're gonna have to bite the bullet and take it apart. You definitely have a vacuum leak of some sort, and there are only so many things that can leak. Make sure your throttle body is closing all the way. Check your egr gasket(s), your throttle body gasket, and your upper intake manifold gaskets. Hell, it's even possible that you cracked your LIM gasket.

What about that stupid little gromet on the pcv line behind the throttle body? That little bastard has given me trouble more than once.

[logikfive]

Well, when I was looking for leaks I had it running around 1,500rpm. Correct me if I'm wrong, but if it is a vaccum leak big enough to make it idle that fast, wouldn't the sucking noise be very identifyable?

I really don't want to take it apart, however, if I can't figure it out without, I guess I will have to.

Thanks for the help!

[tractorman]

Yeah, you'd think it'd be big enough to hear... but your problem sure sounds like a vacuum leak. Don't know what else to tell ya'.

[sharkey]

find out what codes you have, and fix those problems first. whatever the codes are, they may be causing some sort of failsafe mode, and it may cause it to ide high.

[rx191]

it depends on where the vacuum leak is if it is under the intake you mite not here it. pull the air intake boot off a spay a little carb cleaner in the intake and see if it revs up or dies down. if you have a maf sensor don't use starting fluid it will combust. it doesn't take a very large vacuum leak to rev it 1500 but it takes a pretty good one ot go to 3000, what kind of vacuum do you have when it is running to, you could also have an iac problem, put your finger over the port on the front side of the throttle body and see if the rpm differs any. if none of that help pull codes and see what you get. also check the throttle cable and make sure you have it in the throttle body all the way, one of guys at my work had in there wrong and it was causeing a high idle.

[logikfive]

The vaccum is a steady 20 pounds at 1,500rpm. I've replaced the IAC, and did notice after I swapped the IAC off my other Lumina ('95 3100) that the idle came down to approx 1,100 and stayed there until I shut the car off and started it agian. I could not get it to idle slower than 1,500 after that.

I'm also having it thrown on the scanner either Wednesday or Thursday. Hopefully that will point me in a better direction

[bszopi]

I know this is probably way out there, but have you checked to see if the throttle plate is closing all of the way? There is a chance that the shaft or cable, throttle stop screw, or even the plate is stopping the plate from closing completely, which is causing the air to slip by.

If anything, its a real simple and cheap check.

[logikfive]

I know this is probably way out there, but have you checked to see if the throttle plate is closing all of the way? There is a chance that the shaft or cable, throttle stop screw, or even the plate is stopping the plate from closing completely, which is causing the air to slip by.

If anything, its a real simple and cheap check.

I'm pretty sure it is closing all the way, though I'll duuble check.

[91BerettaGT]

I know this sounds absolutely obserd. But do you have floor mats? are they touching the pedal in any way?

(thats the first obserd sounding problem i see lol)

Second thing obserd.

I had a 2002 Impala with this SAME EXACT problem.

We had 2 bad PCM's and 1 bad BCM.

The Body control module was sending the wrong information to both of the PCM's causing the problem.

Now I do not know if in 97 a Lumina had a BCM. But i figured it'd be worth a shot.

It's casually raising idle right? if you put it in drive it could drive itself?

We assumed vacuum leak and instead of digging in replaced the block with one from Jasper engines. Same problem same day as we fired it up. We sent it to the dealer and they spent 1000 bucks on labor alone figuring it out.

[tractorman]

Here's you a slightly less absurd suggestion. I'd go spend a couple bucks and replace that PCV valve just for the hell of it. Plugging it shouldn't make that much difference in the idle speed.

[logikfive]

It has floormats, though I took them out before I even started the car (cleaning them) so that isn't the problem. I'm not sure if they even have a BCM, I seem to doubt it though. Yup, it is a reasonably slow climb to it's desired high idle speed. I myself cannot picture it being a vaccum leak, as it holds a steady 20psi at 1,500rpm.

I put a new PCV valve on it already because the original that was on the car had an abnormal rattle (not the rattle they make when you shake it, but when it was installed on the car)

I'm still stumped on this thing.

[95supremesl]

This is a little late but what the heck. I too experienced high idel at start up and engine check light on.
Finally found the problem. Trace the line from the PVC valve to a T junction on the manifold. It appears that over time the lower half of the T piece has eroded leaving a monstrous gap and causing a vacuum leak.
Repalced the entire section and all works well.