Too fast idle

Hello,

I would try to clean the throttle body here are two guides to help us out

https://www.2carpros.com/articles/engine-idles-too-high

and

https://www.2carpros.com/articles/throttle-actuator-service

Please run down these guides and report back.

My throttle bore was filthy! all fixed love this site.

My 2001 Buick Century has approximately 85000 miles. It intermittently goe sinto a very high idle and after driving for awhile, starts shifting rough. These two do not seem dependant on each other, but each is becoming more frequent. The high idle occurs in the mornings when first starting. If I shut it off and restart a couple times, it will idle normally. It also happens while driving down the road. The rough shifting usually occurs after driving a bit and seems to be more prevalent in warmer weather.

I also want to add that the Service Engine Soon light comes on intermittently and when shifting hard, sometimes it makes a whining sound.

Thanks again.

My question is, what does this sound like to you and in your opinion, what would be an average cost to repair this?

Thanks for your time.

thankfully you have a check engine light coming on, so we wont have to take complete stabs in the dark.

start with pulling the codes and report back.

https://www.2carpros.com/dia/how_to_scan_trouble_codes.htm

Hello, I have a 99 Buick Century and recently I have experienced very high idle speeds and erratic shifting issues. I have cleaned the IAC valve, and did notice my throttle body was rather dirty on the inside. I had cleaned the throttle body with a cleaner, cleaned the IAC, and started the car. The idle was still high. I disconnected the IAC, the TPS, the air box sensor, the sensor on the air intake tube and the EGR sensor, I thought the car should have shuddered or something, so it ran high still. I connected all the sensors back, started the car and still high. My next thought is to disconnect the IAC alone, then the TPS alone. Is there anything I am missing? I have seen others with the same problem, but have not seen any sort of resolution. I thank you for your assistance.
Dennis

The tps can cause a high idle and a hard shift.Did you clear codes after plugging everything back in?

I have not cleared the codes yet. I will have to go to Autozone to have them cleared. I also found the fuse for the O2 sensor was blown too. Might be possible I have bad sensors

if the codes are not cleared will it still have an effect on the idle speed? The check engine light seems to come on and go off intermittently

The blown fuse might have just been a shorted wire to the exhaust etc?Clear the codes and see which ones come back?Let me know the exact code numbers not code descriptions.

ok

Keep me posted.

Codes: p0134,p1635, p0401, p0101, p0108
To negate most of these prior to these codes the only one
I knew was probable was the O2 sensor code due to finding a blown
Fuse in the engine elect panel. I had disconnected every electrical
Connector on or around the top of the engine near the throttle body (map sensor, tps, iac, egr). A total of 5 connectors to see if there would be a change in performance and there was none. The one thing I have ordered is the PVC line assy because its bad. Won't tell you what the previous owner used. Would this line from the evap canister to the PVC cause this problem or do I have issues with the iac or tps? The iac was cleaned with no change less its internally shorted.

So the codes you listed are the ones that came back after you cleared them after plugging everything back in?Also you have a tee off the pcv hose that feeds vacuum to the evap canister purge solenoid?If that hose is leaking that would cause high idle etc.It shouldnt go directly to the charcoal canister or that will cause a problem also the vacuum flow to the canister is controled by the solenoid.Make sure the solenoid isnt stuck open?

I cleared the codes today. I've ordered the evap/PVC hose an it should arrive tomorrow. So I'll know what happens. That hose caused my problem?? Guess ill see tomorrow.

If its leaking vacuum it can cause a high idle etc.

Will let you know definitely tomorrow. The PVC connector end looks like a plug boot cover that was put at the end of the tube. It also causes a whistling sound I think the boot that was used I too soft and causes the "cap" to collapse hense the horrible sound in the engine compartment.

That sounds like a good start keep me posted.

Replaced PVC tube, idle is much better. Computer must still be learning fuel mixtures and shifting is much better with some sluggishness. The old hose was loose on the vac connector from the vap solenoid. Will see how things work out after a few trips. I do still wonder about the IAC. the maintenance manual shows the removed position of the actuator so ill look into that next b

Try taking the negative battery cable off for about a min then put it back on and see how it works then.

Codes cleared still high. Will look at possible bad IAC

Have we looked for more vacuum leaks?What about the coolant temp sensor have.we looked at that yet?

Coolant temp is relative to engine performance. The temp at the moment never goes over half way

I have seen cars with no symptoms of overheating etc with a failing coolant temp sensor causing a high idle.

Ok will look at that next

The codes did clear when I disconnected battery but did come back. I suspect the bank1 o2 is still bad cause the fuse is again blown. This o2sensor is not easy to get to unless I pull the ignition control module and coils.

What is the exact code number its setting now?

Will relay later. Also disconnecting IAC DOES NOT change idle issue

have code 507 and replaced the idle control valve, did not work and the car stalls so i pulled the lead from the egr and set the idle manually and it works but still idles very high and if i plug the wire back in it stalls

You should never adjust the idle stop screw on that car the iac controls the idle speed.You have a vacuum leak somewhere causing the idle most likely.

If you unplug it it cant change the idle keep me posted.

thank you, if i replace the egr and clean the egr line do you think that would help, i intend to replace the air idle valve when i figure out whats wrong and had it replaced already to no avail and was told that my ecu needed to be replaced which i knew was false and was confirmed by another mechanic while getting an oil change who told me after checking on some websites that i would be the first in the country to need this repair, i need to do the repair myself as money is very tight right now

But how long does it take the computer to respond to the idle setting's return to normal?

If the egr valve was not working correctly you would get a egr code.Also if the egr port was clogged it would set a egr code and wouldn't cause the high idle from a clogged port.You said in the first post you replaced your iac valve now your saying you will replace it when you find the problem.So did you replace or not?Also if you had it out did clean all the carbon of its air passage way so it will get a good seat?

Shouldnt take that long.

when the idle was replaced the car stalled and a mechanic set it manually and pulled the wire off the egr so i bought another new idle and and put it in and the car idled fast so i took it out and put the idle that was set manually back, i was wondering if the egr could cause a high idle and why does the car stall when the idle is plugged into the egr

I'm looking for a good diagram for the vacuum lines and don't see one. Besides the one on the hood of the car, is there another one?

When you put a new iac valve in the car will idle high and then the idle will slowly go down until the computer sets the correct idle speed this is normal.Did you give the computer the time to do this?Also if the guy working on your car adjusted the idle stop screw i would find a new person to work on your car.The egr will cause a high idle and stalling if its sticking but also if they stick they set a code.

More info...
when I check the idle with the car being cold the idle is ok,just rumbling, however when the car temp heats up, it goes high. I can't find a leak in the vacuum system unless the leak is at the vac line that runs from the solenoid to the canister, and the canister is in the back of the car... I did a ohms/resistance check of the IAC valve and it checks good unless the valve is just plain worn out.

problem started this week, was in ohio in cold weather, when car first was started it went to a very high rpm, had to shut the engine down and restart to get it to idle normal. later that day it stalled coasting to a red light, started right back up, drove it to NC with no problems, got here and it did the same thing when i started it the next morning, very high idle rpms, shut it down, restarted it and it was fine, drove it 20 miles and it stalled at a light, restarted , no problem..I also have noticed that on interstate hills, it either has a misfire problem or the trans is not shifting down from overdrive without several trys, mash the gas and it drops a gear and is fine, i drive mostly at high speeds and long trips, 70/90 and 500 mile trips, not much city driving. what is causing it to stall and after sitting all night it has this very high idle when first started, also the misfire or trans problem on hills at high speed when it seems like it is trying to shift down or the engine has a misfire, I cant tell which it is, thank you for any answer you may have

thank you, how do i let the computer adjust and how long does it take, do i run the car or just turn it on, i was afraid something else was going on because i was not aware the computer needed time