Hi All:

I am a little pressed for time so I will make it a quick question.

Background Info:
2002 2.4L Z24
Neutral Idle sitting at 1500rpm (normal should be between 700-800rpm) (car runs a little warmer as a result)
It is not erratic idle
Car runs fun otherwise (I mean while I am driving, no noticeable issues)
No OBD2 codes thrown
Need to do emissions test - computer will not test proceed until I can get idle rev down below 1250rpm

I have checked thermostat, engine cooling circulation, IAC, throttle body...all look good.
I have also cleaned fuel injectors (via throttle body).

I got frustrated, took car to dealership, they said Intake Manifold Gasket has a leak (sucking air in, hence the higher rev). They quoted me $1000.00 for the job. :-(

I am tight on cash, so:

How many hours and how hard of a job?
Is there anything else I can check before going the gasket route?

Any and all help would be much appreciated
Thanks
radarcav

That gasket is like $25 if that, and about an hour worth of work.




“Facts are meaningless. You could use facts to prove anything that’s even remotely true."

Man there are some seriously crooked garages.

I found one near my work that was honest enough to give me a "real" quote. $150 parts ($23.45) and labour (1.6hrs). Thank goodness I actually understand how cars work (sort of) and I never trust anyone when it comes to money.

Lawnmowerracer: Thanks for the input. Your numbers are what the honest garage was using.

I really wish I had more time (and a garage) to do more work own my own.

Hold on just a second before you bring it in. Few comments.

With an intake manifold gasket leak you will have more air in the engine, you will have a CEL light for it running to lean. the manifold gasket is after the MAF so the computer isnt calculating it. It sees the extra air is WTH is going on here??? Check Engine Light going on.

Your car is only two years old, got to be honest with you. Gaskets normally last at least 8 years, I cant remember a car ever being in the shop that was less than 4 years old with an intake manifold leak.

With your high idle that could be the cause of an IAC valve being bad.




- 2004 Cavalier - 124k, owned since new

check you're Throttle Position Sensor. i bet you thats what it is.





Peace Out!!!

Rob S:

I was wondering about that also. But the spark plugs did not show signs of having been used in a "lean run" condition. Mind you, I may have checked the plugs too soon. Also, there was no DTC code (I have a code reader) and there was no CEL on. I checked the IAC valve and saw nothing obvious, but you may be right, it could be faulty. Also, while I agree that gaskets should last longer than the 3.5 yrs that I have had the car (bought it in Jan 2002), I do have 155,000km on the car so who knows.

Enrique R

I will check the TPS. But if the TPS is bad, wouldn't the throttle body be more open than normal. When I checked the throttle body, it looked like it was almost closed (as it should be) at idle.

the TPS measures how much the TB is open. a bad TPS would give false readings and would cause a high idle. it would make the computer think that the TB is open more and therefore would use more fuel.




Peace Out!!!

With the TPS sensor let me give you a littel bit of info here.

The TPS measures how open the TB is in volts, 0.7 is at idle, and like 3.9-4.1 is wide open.

Now if at idle say your TPS was saying 1.1 the idle would be higher, more and fuel and air into the engine, because the computer think your doing x mph, when actually your idling.

I would if I was you change either you TPS. TPS only about $25 last time I had to buy one, was for an older Buick though so maybe its different, but they arent that much.

Manifold gaskets dont break down with miles mainly, they break down with age. Espeically in cold climates, cold weather winter, and hot summer, not staying one temp all year. gaskets last longer in the South than they do in the North.


- 2004 Cavalier - 124k, owned since new

By the way if you did have a manifold leak you WOULD have a CEL. These computer are extremely sensative. Did you know from the year 2000, the computer must be able to detect a vacuum leak 1/40 on an inch, about the size on a fully sharpened pencil tip.




- 2004 Cavalier - 124k, owned since new

Thanks for the info everyone.

I tried a few more things.

Using my finger, I plugged the bypass hole in the throttle body (the hole that lets air in for idleing, the hole that should be regulated by the IAC). I was able to stall the engine. So I figured two things:

1) Intake manifold gasket problem not likely since I can stall the engine
2) IAC may be screwed

This morning I went and bought a new IAC ($150CDN, non-returnable). Swapped in the new one....no difference. DAMN!!! So I do not believe it is the IAC valve.

I figured ok maybe it is the electrical harness to the IAC or the PCM. I doubt it is either.

If the TPS is that cheap then I will try that. I am still not sure I understand how a bad TPS would let more air in. The butterfly valve (throttle plate) basically looked closed at idle, so the (extra) air would enter where? Through the bypass valve that is controlled by the IAC? Or am I just blind and the butterfly valve is actually more open than it should be.

the tps doesnt let more air in. it makes the computer think that the tb is open and therefore makes it spray more fuel into the engine. and yes, the extra air it needs does go through the bypass hole. trust me. its your tps that is faulty. i've been through this exact same situation. i checked everyhing i could. fpr, map sensor, iac valve, and nothing changed until i got a new tps.






Peace Out!!!

Sounds god Enrique R. Thanks for the help...I do appreciate it.

At lunch today I will measure the voltage at idle at the TPS and see what I get.

Well I checked the voltage at the TPS.

Idle = 0.45V
WOT = 3.92V

Now I an really stumped!!!

well, im sticking to my resolution. but, wow. i just noticed the quote for the manifold gasket. haha. thats ridiculous. i've taken mine off and it took me no more than 30 minutes to take apart and the gasket comes off easily and the new one clips onto the manifold. i'd change it out for you for $20, lol. good luck with your car though.




Peace Out!!!