Different Idle Speed After Changing Intake Manifold Gasket - Corolland: the Toyota Corolla Forums

This forum was great help for info on replacing an intake manifold gasket. The only part i would mention is that the 2003 2004 Corollas have a different throttle body mechanism than the ones on the posts here. That threw me off a little. I won't find out till this winter if it solves erratic revving in cold temps but i hope so.

I cleaned the throttle body and changed the air cleaner before restarting the engine. It revved to 2000 rpm for a few minutes. then it revved up and down for 5 more minutes. Now it takes 5 minutes but when warm it will settle on a steady 1000 rpm idle and runs fine. Is all this normal? Before gasket replacement it idled at 700rpm steady. Is 1000rpm a good idle speed?

You did reconnect the brake booster vacuum hose behind throttle body? After battery is disconnected, it can take some driving time for ECU to relearn operating conditions before idle settles normally again.

Thanks, I checked and all hoses are connected. I did not disconnect the battery when i did the job because i cancelled the code with a code reader. Is 1000rpm the right idle speed? Should i disconnect the battery now and hook up again?

It sounds like you now have a vacuum leak... Something or a vacuum hose must have been overlooked.

Pic shows elusive brake booster vacuum hose on intake manifold fitting, which is hidden once throttle body is installed:

Thanks for the reply

I checked and all hoses are connected. It starts now nicely. It takes about 4 minutes sitting to get to 1000 rpm idle steady no jumps. Seems good to me. Is this now normal? 1000 rpm is the right idle speed? If you think i still have a vacuum leak are there any tricks to finding one and stopping it?

Idle speed should be printed up on a placard under the hood. True, after resetting the ECM - you have to give it a little bit of time to relearn parameters - but that should be relatively quick. Normal day of driving should do it for more people.

High idle, as mentioned earlier - is most likely a sign of a vacuum leak. Could be a loose or missing hose, cracked/damaged hose, defective new intake manifold gasket, cracked/damaged/warped intake manifold, incorrect torque on intake manifold bolts, etc.

Might try an old school trick - use a spray bottle of water mixed with a couple of drops of detergent - start spraying the hoses around the intake manifold and the throttle body and intake manifold itself - all while the engine is running. If the idle changes anywhere you spray - that is the source of the vacuum leak. I personally like water - easy, won't damage components unless you soak then beyond a reasonable level. Some people prefer to use brake cleaner, carb cleaner, starting fluid, WD-40, etc. - while OK in small amounts, the solvents all tend to do some nasty stuff to plastic and rubber bits - WD-40 leaves a film that can soften some gaskets/attract a lot more dirt.

My 2004 manual idles at 750 rpm, as it should.

friendly_jacek

Thanks, I checked and all hoses are connected. I did not disconnect the battery when i did the job because i cancelled the code with a code reader. Is 1000rpm the right idle speed? Should i disconnect the battery now and hook up again?

Yes! you need to reset engine ECU to relearn new correct idle spead.

You can remove the blue 15A "FI" fuse in engine bay instead of disconnecting battery, but I doubt it would help.

hey fish, isnt that the trick for finding a positive leak ( i.e. tire or rim) ? That mechanic on youtube Scotty Kilmer showed a great trick for finding vaccum leaks..usa 99 cent cigar..the cheaper and smokier the cigar, the better.

Yeah, similar trick for finding leaks - just add a bit more detergent to make sure it bubbles up when you hose down a suspect positive leak. Smoke works OK, if the leak is big enough - or if you are looking to get your nicotine fix + work on the car at the same time! A twofer!