3.9k idle after cleaning upper and lower intake [Archive] - GrandAmGT.com Forum

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MercenaryX2
11-30-2012, 08:48 PM
Title says it all. I scrubbed the TB, upper plenum and lower intake with some carb cleaner and a tooth brush. Went to start it to burn the cleaner sitting in the runners/combustion chambers and gave it some gas to keep it running. I figured I would have to give it gas for a little while to burn it off, as if you were to SeaFoam the engine. Well even after driving it around the block, it still wanted to stall.

Limped it back to my apartment, shut it off and let it sit for a few minutes. Turned it back on, stumbled and I still had to give it some throttle to keep it alive, then all of a sudden it shoots up to 3900 RPM's and won't come down. Even after starting it up again, it immediately goes to 3900. Checked the throttle plate for it sticking, checked the torque on the bolts for the upper plenum. Oh I unplugged the MAF and it still did that high idle. No change.

Tips? I couldn't imagine it having a bad enough vacuum leak for this to happen and with it having 161k miles (granted all I use is synthetic oil) I don't want to let it just sit there and idle that high to see if it will come down. I'm pretty mechanically inclined but for some reason I can't figure this one out. Its not my only car but I do need it running ASAP.

Thanks in advance guys.

AaronGTR
12-01-2012, 08:20 AM
Well, first off you shouldn't ever clean the lower intake runners while it's on the car. You don't want all that crap running down the runners and sitting behind the valves and leaking into the cylinders. It can't have done any good for the pistons/rings etc and might even cause a valve to stick or something. If you want to clean the intake runners at all (which they probably don't really need) you would be better off using seafoam like normal, and running some fuel system cleaner through the injectors. Also if you pulled the upper intake to do this, did you replace the gaskets? If not, that could be causing a vacuum leak.


As it is, I'm thinking you might have damaged the LIM gasket. Carb cleaner is pretty aggressive compared to brake cleaner or other things, and it will eat away some plastics. If it damaged the LIM gasket and it broke somewhere, you'd have a massive hole in the runner that would be bypassing the TB and pulling air from the lifter valley area which would pull air through the PCV system, which comes straight from the intake in front of the TB.

Time to start taking the engine apart.

MAC the KNIFE
12-01-2012, 05:35 PM
maybe if the IAC valve is stuck wide open. not sure its big enough for 3900rpm though...

if it wasnt stalling at first, then i'd swear you had the throttle cable wrapped around the guide wrong, or caught on something

MercenaryX2
12-03-2012, 02:20 PM
Okay I may have to try replacing the LIM gasket. I just went out to the car a little while ago and it still wanted to do it. Unplugged the MAF, still the same. Plugged it back in, now it wants to bog out again. That should mean atleast the MAF isn't fried right?

Aside from that, yeah I'll have to buy a lower and upper gasket and go to town.