High RPM's Followed By Rough Idle, I Can't Figure It Out.

[tunernewb92]

Me and a friend have a 92 Eagle Talon TSi AWD. It is bone stock, no mods, not even cheap mods. We just bought the car from a co-worker. The car has a major problem though at start-up that I would really like to fix because I'm afraid to drive it anywhere. When we crank the car up, from either cold start or warm start, the RPM's shoot up to about 2000 for ~5-10 seconds, then slowly dip back down to below 1000. When it gets to ~1200, the car starts to idle bad. I mean really bad. It sounds like it has a misfire, the car literally shakes, the engine seems like it is fighting to stay alive. My best discription would be like an older person with a really really bad cough. I searched and didn't find anything that sounded exactly like this. I was told by a friend that it was timing, but once you get the car moving it runs great no misfiring at all, or none that I can tell. I have new sparkplugs but I haven't yet put them on. We know the headgasket is leaking a little and we've heard that a leaking headgasket could cause a rough idle, but this bad? I messed around with the BISSS yesterday and it still did the same thing I described above. Is it the timing belt? Any suggestions would be great at this point.

EDIT: Car has 240k miles on the original engine, but not the timing belt, it was replaced about 4 years, 60k ago.

 

[360glitch]

As co-owner of this car I though I should chime in. After doing some research last night I think the next step of ours needs to be to check the ISC. Yes, we know we need to do the timing belt soon. Thanks for the help.

 

[90laserRSfwd]

A compression test, fresh plugs (for your car I'd say a set of NGK BPR6ES plugs gaped to 0.028") and wires are most likely in order. Possibly a semi clogged fuel filter could be a lead to follow up as well as the ISC liked mentioned above. Although if the idle is stead (rpm wise) but just choppy (like a misfire) then I'd look into plugs / wires and a fuel filter first. Remember this cars are stubburn. (maintenance is key with these cars). Also like mentioned Timing and Bal. Shaft belts are do very soon, don't forget the water pump!

~ Jayson

 

[99RedGs]

Did you check for vacuum leaks?

 

[tunernewb92]

eh...yes we checked them as best we could last night.....we can hear a hissing sound that sounds like vaccuum.

Has anybody ever heard of spraying a little H20 or carb cleaner around the vaccuum lines and seeing if the engine sputters to find the vaccuum leak?

 

[360glitch]

eh...yes we checked them as best we could last night.....we can hear a hissing sound that sounds like vaccuum.

Has anybody ever heard of spraying a little H20 or carb cleaner around the vaccuum lines and seeing if the engine sputters to find the vaccuum leak?

Ok, tonight we diagnosed the ISC to be defective. Hopefully that is all there is to the story but I'm not going to get too far ahead of myself. How big of a deal is it to swap the ISC out?

 

[srumel]

It's not bad at all. Just a couple of screws and an o-ring gasket; that's about it.

 

[Jimmer307]

As mentioned above, i would change that timing belt ASAP. When that belt goes so does your head, and your going to have a ton more problems than a rough idle. As for your idle problem, that sounds like the ISC. I just replaced my a few thousand miles ago and its really no big deal. Its pretty much a 5 minute process

 

[tunernewb92]

went and pulled the ISC today and we will change it tonight, could a leaking head gasket mess it up this bad?

 

[spydermanX98X]

Sounds like you should clean the throttle body really well too, alot of times when a car is "hunting" for an idle speed, like moving up and down in the RPM range it's because of a really dirty throttle body.

 

[ClevelandDSM]

"Has anybody ever heard of spraying a little H20 or carb cleaner around the vaccuum lines and seeing if the engine sputters to find the vaccuum leak?"

I do this with carb or break cleaner at work sometimes to see " if " it has a vacuum leak. Will cause the engine to surge. Just dont use a ton, and its just to test the semi-location, not the exact spots and such.

 

[tunernewb92]

Ok so we replaced the ISC and the sparkplugs....the number 1 cylinder had about 2 cm of oil in it....and adjusted the BISSS screw.....the Idle has dropped to around 1200-1500. It will continuously climb to 1500, then drop to about 1100-1200, then go back up and back down pretty quick. It sounds like its dying while its dropping to 1100 and it sounds pretty go on the way up to 1500. Tomorrow we will replace the head cover, head cover gasket and the spark plug gaskets....Any other ideas, is this still a timing issue?

 

[voodoogsx]

I've had something very similar with a vac leak....it's been the lines in the area of the TB.
Check for cracks in the vac lines or just replace all of them with some new stuff to get that all out of the way.
The other thing would be to make sure that the wire harness on the mass is connected and tight, that can cause some odd idle issues as well. Check the recirc dump tube to make sure you're not venting anything their as well.
For most of these things you might want to try some soapy water to see if any bubbles appear.....