A common 3.4 GTP Problem that seems to lack an answer

[Phill Acio]

Ok I have a 94 GTP with a 3.4. Im having problems with it idling. My car seems to enjoy idling at 2000 rpms for some reason. It doesn't do it all the time. It really has a hard time ilding when it first starts in the morning. It will jump up to 2000 then down to 500. It will either die or ilde back up. It will search for an idle then eventually run normal for alittle bit. While im driving it will either idle high or run normal and every once and a while the SES will come on, but only for a little bit. When it is idling high it is running real ritch. I can smell the gas comming out of the exhaust. Any information would be greatly appriciated.

[rockford0384]

sounds messed up. I once had that same engine in my old GTP and It would idle high like that when it first starts up and sometimes it wouldnt even want to start. I dont know if this would help out any ... but change the fuel filter... That seemed to be the best thing i ever have done to that car to make it run good. It had 157000 miles on it when i sold it. It finally died though at 178000 miles! Thats crazy for that engine. anyways im not sure really whats you problem. sorry

[RABarrett]

Several things come to mind here. There is the possibility of a vacuum leak. There is also the possibility of the need for a thorough throttle body and IAC cleaning. I would check for vacuum leaks first. Ray

[GMMerlin]

Those engines are known for developing vacum leaks at the PCV hose and the intake manifold.
I would check those places first.

[winaukee]

Lucky for you i have the answer to your problem. I had the exact same problem until i replaced my upper and lower intakd gaskets. That will take care of it for sure!!!!! cost about 350$

[BLOWN_GTP]

your problem is the intake gaskets. Turn your car on and pull the 3.4 plastic cover off and spray some TB cleaner around the intake. That is a cheap way to diagnose the problem right there because if there is a leak when the spray is applied your rpms will fluctuate. Upper and lower intake gaskets are an easy job. Dont let the 3.4 motor scare you because of the size. Unfortunately it scares most people into selling it.

[kilroypr]

I agree, check for vacum leaks and also clean the intake trhotle and IAC hole clean of the black dust.

[twstice]

im new here, and ive got the exact same problem with my '95 grand prix gtp 3.4L DOHC. i replaced the throttle position sensor thinking it might be that, it didnt change.(i read in another post that i might have positioned the sensor wrong, so that might still be the problem). i also tried replacing the idle air valve sensor, b/c sometimes when i unplugged it the engine would idle like it's supposed to for a while..., i replaced the idle air valve and it did not change with 3 different valves. i recently tried replacing the intake gaskets, but i only replaced the upper gasket. it still did not change how the engine runs. should i maybe go ahead and replace the lower intake gaskets as well??? or what should i do??? i will have looked all over the place for a vacuum leak and as far as i can tell there isnt one, i might have over looked one though. PLEAS HELP, i cannot seem to figure this out.
thanks ahead of time,
-Trevor

P.S.( i just noticed this is a rather old thread, i hope someone notices this)

[JGTP94]

I had the same problem in my 94 GTP and Believe it or not INTAKE gaskets... A very common problem in these engines i hear just not one thought of much. mine did exactly what u discribed and once it was fixed it now runs perfect no idle probs

hope this helps...

-Jason-

[twstice]

ok, i will go ahead and replace the lower intake gaskets as well. i hope it works, thanks.
-Trevor

[dopey273]

My gtp did the same thing.. pull the engine codes. mine came up with the o2 sensor. what would happen is it would be erratic sometimes runs fine sometimes not, you could smell the gas. the ses light would come on intermittently also. What was happening was the o2 wasn't registering properly, it would read lean then the ecm would try to fix it by adding more fuel, when it did that , then it read rich. I replaced the o2 sensor, which i had to remove the top plenum to do it, and it fixed the problem, I even got better performance and fuel mileage... I would suggest getting the engine codes pulled first before doing anything though....

[slacker_53]

As stated in a previous post, spray some WD-40 around the intake while the engine is running. The idle should change a little if you have an intake leak, when the engine picks up the WD.

Cheap and easy, just like my girlfriend.

-slacker

[JDLB]

I have the 3.4 DOHC in a '92 Cutlass Supreme that has the same problem. I already changed the IAC and upper intake gasket, but it still runs at 1500-2000 RPM's when i start it, and then it will sit there and pulse the RPM's when in drive or reverse. I can't figure out the problem.

[MoDoggie]

Originally Posted by JDLB

I have the 3.4 DOHC in a '92 Cutlass Supreme that has the same problem. I already changed the IAC and upper intake gasket, but it still runs at 1500-2000 RPM's when i start it, and then it will sit there and pulse the RPM's when in drive or reverse. I can't figure out the problem.

I have the 3.4 DOHC in a 94 Grand Prix GTP and when I bought it it had a serious idling problem. I changed the intake gaskets and that fixed it. Then I just recently tore it down to the block to fix an oil leak at the oil pump drive shaft (distributor). Now that I have it all back together I am having problems with it staying running. I will start but idles very rough not erratic like before and once it warms up it will stall out when idling whether in gear or not. I have checked for vacuum leaks and have found none, not sure if it is a sensor but the SES light did come on once, but has since went back off. Any other ideas???