Mechanics

HIGH IDLE ISSUE AND INTERMITTANT SHIFTING CAUSE IAC, TPS?

1999 Buick Century • 170,000 miles

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
Avatar
Dlvaughn1963
September 24, 2012.



I will look again at the purge solenoid. I remember the connection but not sure how many hoses I saw. More to come

Tiny
Dlvaughn1963
Sep 28, 2012.
Alright keep me posted.

Saturntech9
Sep 28, 2012.
After looking at a photo of the EVAP purge valve/control solenoid, I'm seriously considering this specific area to be my problem and here's why. When I first replaced the hose from the PCV to the solenoid, the idle issue surged then immediately went to normal. This was fine for about half a day, then surged back high. I think I also told you I had replaced the PCV on this same day. I do hear hissing like from a vacuum leak but the place where this valve/solenoid is located means I need to use a mirror to see and repair/replace. According to the manual, and internet searches, there are two hose connectors. Which one goes where? I'm not sure if I have seen the hose for the other connector, and I will verify that today. All I know is this car eats gas now as if I have a bank account just to feed it (lol). Anyway I will let you know what I find out.

Tiny
Dlvaughn1963
Oct 1, 2012.
Update.
Here's what I did this morning.
1. Checked coolant and topped off
2. Checked the ecu fuse was good.
3. Started engine, idle still high so
I disconnected PVC line checked for vacuum, was good
Disconnected fuel pressure regulator line, vac good there
Checked booster vacuum, good
visually checked the vacuum lines on Purge valve solenoid, all connections good, and disconnected power to the valve.
4. Shut engine off. At this time the only connector not connected in the engine compartment was the purge valve solenoid.
5. Started engine, still high, connected solenoid valve plug, let run for about 1 minute, then shut off engine.
6. Restarted engine and idle returned to normal. Run A/C, Shifted transmission from park through selection ranges, still normal idle, back shift back to park, and idle still normal.
My synopsis is that when I had the bad PCV line to the solenoid, after a bit of time the solenoid stuck in the open position because of vacuum failure (would that be a correct guess?) By resetting the solenoid, the operation of the part went back to normal operations. What I thought was a vacuum leak was not, I wanted to find out if there was an issue of vacuum and the Evap service line did not give me any indication of a leak there either even with the engine running. I will let you know if anything else happens, but for now all seems well.

Tiny
Dlvaughn1963
Oct 1, 2012.
If the canister purge solenoind is stuck open it can cause high idles dieing etc. The vacuum leak is just happening in the gas tank. When you have the idle see if the valve is stuck open.

Saturntech9
Oct 1, 2012.
That also would explain why my gas level fluctuated as much as it did. The idle did sneak back up. I purchased a new purge solenoid. Will change it next.

Tiny
Dlvaughn1963
Oct 1, 2012.
I did get the purge solenoid changed. Idle is good. I did hear hissing near the tank, not noticing this before because I've gotten like really picky about the noises my car makes lol. Is the hissing sound normal?

Tiny
Dlvaughn1963
Oct 1, 2012.
When do you hear the noise after tuning the engine off?Where is the noise coming from?

Saturntech9
Oct 1, 2012.
When the car is running.

Tiny
Dlvaughn1963
Oct 1, 2012.
So is this after the car has warmed up and this was after you changed the solenoid?

Saturntech9
Oct 1, 2012.
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