2000 SL2, 125k miles, occasional 1500 rpm idle after intake replacement
 

Hi all,
Thanks for taking the time to read this and offer any advice you may have.

I've got a 2000 SL2 with 125,000 miles on it, (bought with 80k), that I recently replaced the intake manifold on (crack in small coolant tube that was leaking fluid) with a pick-n-pull intake from an '02 SC2. It didn't have this occasional high (1500 rpm) idle before, but now it happens at the end of a trip every now and then. Normal idle is at the normal 850 rpm. I thought I did a good job replacing the gasket with a new OEM I ordered on ebay, oiling it up well, and sufficiently scraping off the old gasket from the engine block and cleaning the mating surfaces.

From some threads I've found here, it looks like I want to spray some carb cleaner around the intake and see if that changes the idle, revealing a leak and the need to replace the gasket.

From my Chilton, I also found that I can spray carb cleaner in the throttle body intake to clear any gunk that might not be letting it seal properly and thus affecting the idle. I did my best to clean it with rags/paper towels and q-tips before installation but despite this the replacement throttle body intake was indeed still a little more gunky than my original.

So bonehead question here but just to be doubly sure: there's nothing wrong with spraying carb cleaner down my throttle body intake or around the intake manifold while the engine is running? I'm hoping I can just clear up the throttle body intake and that will fix the problem, and not have to remove and replace the intake again.

Thanks for your input,
Cade

Spray away keeping it close to the mating surfaces.

OK thanks,

another nugget of info: it did it last night when I was pulling up to park and I just immediately turned off the engine, turned it back on, and the problem was gone. Does that offer any insight?

Not really.

That can be a symptom of a bad throttle position sensor.

CAN be.

Clean the throttle body, especially the back and edges of the throttle plate, where the edge of the throttle plate would touch the bore of the throttle body when completely closed if it did actually touch.

Also be sure to clean the IAC.

It's a very old car with a very old throttle body.

And to add to what derf said, use throttle body cleaner and not carburetor cleaner. Carb cleaner will strip the coating off the throttle body. Or so I've read on several car forums.

If it idles SMOOTHLY at 850 you have no vacuum leak.
How much oil does it burn per 3,000 mi?

Vacuum leaknis causing the high idle.
 

smoke test your gastank. I had to run my machine for the full 5 minute cycle, and then mysteriously smoke started coming out around the filler neck and pipe. All the plastic has dried seals or is becoming pourus. I pmegged the line going into the back of the throttle body on both sides. Never had the high idle again.

Hi Derf,

I just checked my dipstick after 500 miles, and surprisingly, it needed a liter of oil. I feel like in the past it has been a liter every 1,000 miles. Granted, I live in a town with a lot of topography, and in addition to my brakes I use my engine to hold my speed down hills and decelerate, and sometimes like Jimi Hendrix in "Crosstown Traffic," "Ninety[plus] miles an hour, [baby], is the speed I drive." In times past I've kept my miles really mellow by keeping speeds at or below even 55 mph, thinking I'm preserving the life of the car, and I feel like then it was using 1L/1,000 miles. I see some oil staining around the filler cap, is this where I could be losing oil? I don't understand "burning" oil, and my dad says there's no such thing, it just means that I'm leaking. Thing is, I check under my car and there aren't any leaks.

Anyways, thanks for your time. Appreciate all the input.
Cade