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
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Dlvaughn1963
September 24, 2012.




Sounds good keep us posted.

Saturntech9
Oct 4, 2012.
Where is purge solenoid located? I'm doing the EGR valve now (it started raining, took a break). Last night while looking at it seemed to be the source of the "whooshing" sound. It's about the only old part left.

Tiny
Greghoward
Oct 4, 2012.
The canister evap purge solenoid is just behind the egr valve. Follow the pcv hose behind and under the ignition coils(if u have the 3.1 eng). There are two vac lines one from the pcv the other goes to the evap canister.

Tiny
Dlvaughn1963
Oct 4, 2012.
Thanks

Tiny
Greghoward
Oct 4, 2012.
At a loss. Now what is happening is the engine performance is really bad. When starting, the engine runs extremely rough to the point of stalling. When the engine is shut off and restarted repeately, the problem does not go away. Although when letting the car sit idle for about 5 minutes the idle is then fine. Do you remember telling me something about the coolant temp sensor? Would this be my culprit?

Tiny
Dlvaughn1963
Oct 11, 2012.
Are all the hoses fixed?Do you have any coded in the computer?

Saturntech9
Oct 11, 2012.
You will enjoy this.
I"m not sure what fixed the idle issue but, it is gone. Possibly combination of repairs
1. PCV
2. PCV vent tube
3. Evap canister vent solenoid
4. IAC valve
5. Cleaned EGR Valve.

Now I have no codes except for a random engine misfire. My goal at this point is to replace all the wires. The coils all have good fire and I'm not sure what plugs/wires age are at this point. So I will go there. I pray the injectors are good, but that is another issue.
I did have my codes checked at autozone and a P0300 and P0404 hence why I cleaned out the EGR Valve and replaced the seal/gasket. As of Now, I have NO codes. Repeat NO codes from the engine. Even the cylinder misfire code 0300 has not resurfaced. More to come.

Tiny
Dlvaughn1963
Oct 12, 2012.
Wow you went all out on that engine lol keep me posted.

Saturntech9
Oct 12, 2012.
I replaced the EGR valve and the Buick ran perfect. The rough idle and poor gas mileage went away; it ran like a dream all week. Today my mom called and told me that the rough idle has returned. Why on earth would it run great for a week and then go right back to having this problem! As I said before I had rebuilt the engine from the heads up a few months ago, the EGR valve was the only part I had not replaced. It was running better than new up until a few weeks ago, now, like you, I'm stuck with this mysterious problem. It runs fine, plenty of power and smooth, but it's idling rough and losing gas mileage. This is getting frustrating!

Tiny
Greghoward
Oct 13, 2012.
Here's the situation at this point
I have replaced all 6 plugs
four broke at the ceramics, two had worn tips but suspect bad gap and just old plugs. They had Autolite 606 plugs.
Got the new plugs in, starts and idles fine, BUT, still have surging and misfiring. When the car is running and I'm driving for about 1/4 mile it runs horribly, but after that, the car settles and runs fine. This happens anytime the car is shut down and restarted. Any other suggestions? I have checked the coils, but they seem to be producing good spark. I will take the coil wire caps off and look at the spark in order and see if they seem to be weak at the cap. Then possibly look into either coil, or bad ICM.
AD

Tiny
Dlvaughn1963
Oct 13, 2012.

AD