Cold idle speed 2500 RPm and miss

[mworke]

Hi,

New to the forum. Son recently purchased a 92 GP wit 3.4l DOHC. Car is clean but when engine is cold it idles at 2500 - 3000 RPM. There also appears to be a miss and an over rich fuel smell from the exhause. Any ideas where to start?

[geldartb]

thats a litte high for the idle. sounds like a vac leak somewhere. check the hoses and intake gaskets.

[mworke]

Thanks......I will check. Last night I pulled fault codes of 32(EGR) amd 35(Idle Air Controler) form the ECM. I'm going to measure the resistance of the IAC valve tonight to check if it is defective.
Mike

[geldartb]

egr probably just a clogged passage from carbon buildup. try and clean the part on the intake manifold out with a piece of coat hanger or something along those lines.

try and swap the iac with a different one if you can just to see if it helps before you spend money on parts you dont need.

as far as the miss goes check the coil pack and if the wires and plugs have never been change it cant hurt to do them.

[GremlinZ34]

my vote is intake gaskets (upper AND lower). I had the same issue on my old 91 Z34, it eventually turned into a full time high idle.

My guess is that when cold the intake gaskets are not sealing correctly. As the engine heats up and the metal expands, the gaskets seal.

[mworke]

Thanks to all for their input. I checked the IAC electrically and it was ok, however the pintel moved in/out 1/8 inch and had excessive lateral movement (Wobble) I replaced the IAC and idel is now at specified levels.

[mworke]

Well......the issue is back . GREMLINZ34 hit the nail on the head. Over the weekend my son was over complaining about the high idle (2000 - 2500 RPM) again. I reviewed this post and checked the intake gaskets again. When the front bank was sprared with carb cleaner the engine settled down and ideled at 800 RPM. As the claner would evaporate the idle speed increased.

I really do not want to replace the upper and lower intake gaskets if I can help it. Has any one tried to seal the gaskets with a thin RTV sealant like the ones used on windshields? If my option is to replace the gaskets, what kind of job am I in for as far as time?

Thanks,

Mike

[GremlinZ34]

Honestly its not that hard to do.

I've done this a few times on my Z34's over the years. You just have to take your time and make sure everything is accounted for. A full uper intake gasket set goes for about $25-30. This includes uper and lower gaskets, the EGR gasket, the o-ring for coolant to the intake and the oil galley gasket. I would also get a fuel injector O-ring set.

This is a very simple and straight foward proceedure and can be done on a saturday or a sunday. Just make sure you disconnect everything needed and make sure you put it back the way you found it.

If you need any help or advice I would be more than happy to help. Just don't use RTV, it could get sucked into the intake and cause all kinds of problems.

-John

[mworke]

Looks like I will be changing the intake gaskets. Is it normal for the engine RMP to drop when carb cleaner is sprayed near the source of a vacuum leak? I was under the understanding that the RPM would increase! Just speaking out load. A co-worker of mine had a '92 GP with the 3.4 and he indicated that it is not that tough of a job - he even offered to assist. What a friend. Thanks all for the input.
Mike

[mworke]

Well....changed the upper and lower intake gaskets wih the help of my friend Chris and that solved the fast idle spped issue. Thanks to all who posted on this ieeue. I now have a different issue that is probably unrelated.

When the headlights are turned on and/or the brakes applied the engine dies. Seems as if the battery is shorting or something like that as the lights in the dash will flicker and everything goes out. I plan on checking the state of the battery tomorrow. Any ideas???

[BlueFlame]

Check the battery for sure, but you might have a problem with the alternator, which would kinda suck, cuz that's not a lot of fun to pull. Mine and my sister's have both done that. Both replaced batteries and later had to replace the alternator, so make sure if you replace it that you carry some cables around in the trunk for a week or so just to be sure. I think there's a write up on pulling the alternator if you have to on here, but if you determine you need to do that and have questions, just hit us up.

[mworke]

Electrical issue is solved!!

A pair of stripped batter cable attaching bolts was the culprit. We replaced the negative cable bolt when we were finishing up the lower intake gasket swap due to the threads being stripped – I never expected that the positive cable bolt was also stripped. Both battery cable attaching bolts replaced and car now runs fine. Thanks to all for their input to this post.

Mike