98 Monte. Over the past month, when the Monte is started, it idles around 1500 rpm. Letting it warm up, doesn't help. Blipping the throttle, doesn't either. Which causes the rig to run around 45-50 mph with my foot off the gas. It doesn't happen all the time. Maybe a dozen times.
Any ides?
Thanks

 

I would say check the idle to make sure it didn't get adjusted up. But if it's only an every now and then problem, that kind of blows a hole in that theory.

 

Carbon build up on the IAC pintle or seat can cause erratic idle. I'd start with removing it from the throttle body and cleaning it.

 

My car idled high and weird when I had a vacuum leak. Worth a try.

 

What engine do you have ? How many miles ?
When was your last major tune `up ? Do you have any codes ? Is you check engine light on ?
I hope the below gives you some items to check..Good Luck

A high idle can be caused by several things.
1. A vacuum leak.
2. Sticking or faulty Idle Air Control Valve (IAC).
3. Carbon build-up in the throttle body bore and plate.

Always have the system scanned for codes first.

 

Engine is a 3.1
112583 miles
New plugs(platinum) @ 80,000 miles(what a pain that was!)
Codes: I don't have a reader
Check engine light not on

Went to check the OHMs on the iac but can't get the plug off. Is there a trick? Or do they just come off hard. I don't want to break the little sucker.
I have the air intake off the throttle body and am going to spray it with cleaner and wipe it out.

 

Things I'd look at (starting with most likely to least):
- Is the car throwing any check engine lights?
- What brand plugs? If they are BOSCH plugs, rip them out. Go with AC Delcos (I've tried NGKs on one car with no prob). Me and my friends have had bad history with BOSCH plugs being crap out of box new OR within 6 months.
- Did you verify the gap on the plugs during installation?
- Inspect plug wires for any signs of damage.
- Check for vac leaks (easy way, with it idling, mist starting fluid around all vac lines and seals).
- Remove the wires (one at a time) from the coil packs. If the metal tips of the coils look "rusty" or cruddy, get a Scotch Brite pad and clean them.
- If you car is equipped with a MAF, buy the MAF cleaner, and follow the instructions for cleaning your MAF.
- Remove the EGR, there is a passage way from the EGR to the upper intake. That passageway can get "gummed" up. Usually it results in an engine code, even if it's not, good to clean it once in a while (50,000-100,000 miles).
- The IAC could be carboned up, not a bad thing to check, but not first on my list to check. As for the connector, it has a tab, gently push it a little with your thumb and then wiggle the connector off.

 

A lot of what you listed to check would (most of the time) create a consistent condition, not an intermittent one. Seeing that it is a problem with erratic idle, the IAC would (imo) be a logical place to start. The next place I'd check would be for sticky/binding throttle linkage.

 

Well, I finally got the plug off the IAC. Ohms checked out within spec. Cleaned the throttle body. It was actually pretty clean. This week-end, I'll take the IAC off and clean it and see if that helps. Of coarse, I have to wait to see if it does it again.

 

Well today I learned a few things from an old friend. I'll share them with you.
My friend and his Ol'Lady rolled in on their scoots Saturday. I was just getting started on removing the IAC. He asked what the problem was and I told him the problem I was having. So, we took the IAC off and It was quit clean. But, we cleaned it anyway. Next he suggested I take the TPS off and check/clean it. I had already taken the TB off and cleaned it.
Then He asked if we had a NAPA store. Got on our pigs and off we went. Got there and he asked for a radiator funnel kit. Part no. NAPA AUTO PARTS
We get back and we hooked this thing up and poured some anti-freeze in it. Start the rig and let it come up to temp with the heater on max, no fan. As soon as the rad fans came on, I start to see air bubbles coming up into the funnel. After a few minutes, no more air bobbles. Shut the engine off and let it cool down. He went to his scoot and got a cigar out of his S/Bs. Lit it, pulled a vacuum line off and began blowing lots of smoke into the line. After a couple of minutes, he hooked the line back up, turned and said, " You have no vacuum leaks.
Then he told me, if the problem returns he'll put all new TPS, IAS, etc and he'll pay. Basically telling me the problem was the air in the radiator.
I guess, I shall see.