Rpm Hunting At Idle

Guss23

Guss23

Active Member
#1
#1
Hello all,
I have a relatively low milage (10,000 mi) TTA. At idle it seems to run rough and starts to hunt between 500&1,000 rpm. It’s has died at idle a couple of times. I am going to put new spark plugs in it today to see if that helps. I’ve been getting the car to where I want it esteticly to start driving it this spring so I’ve put a tank of high octane gas in it and let it idle while I work on it. I’ve probably only put 25 Miles on it myself so far. It runs perfectly while driving and when I rev it up it sounds like a new car. The power is perfect. Any ideas????
 
Guss23

Guss23

Active Member
#4
#4
It seems to run properly for a minute or so and the rpm drops to about 500 and then it bounces to about 1000. Then it starts over again.
 
S

shadow images

Well-Known Member
#5
#5
Not saying this is your problem but we chase a similar problem for a couple of months until the drivers in the computer finally went out. I would check what Robert said above first but if you cannot find anything else try to borrow a know good computer.
 
TTA_PACE_CAR

TTA_PACE_CAR

Active Member
#6
#6
A few possibilities:
Mass Air Flow Sensor
Idle Air Control Valve
Check for any leaks after the MAF sensor and vacuum leaks

Also you say it seems to happen when it's hot would point to a sensor since you would be in closed loop.
 
Guss23

Guss23

Active Member
#7
#7
Ok, I got a new MAF at O’riles and installed it. The car started, ran for a few seconds and died. It did it repeatedly so I put the old one in. The computer is new in it. Tried adjusting the tpi and had no luck. Is there a trick to setting them??? When I changed the spark plugs they were black and very warn.
I’ll try idle control next
 
TTA_PACE_CAR

TTA_PACE_CAR

Active Member
#8
#8
Guss23 said:
Ok, I got a new MAF at O’riles and installed it. The car started, ran for a few seconds and died. It did it repeatedly so I put the old one in. The computer is new in it. Tried adjusting the tpi and had no luck. Is there a trick to setting them??? When I changed the spark plugs they were black and very warn.
I’ll try idle control next

Don't make too many changes at once. Firstly, It's really important to make sure there are no cracked turbo hoses or loose vacuum lines anywhere.

Next you really need a scan tool to look at the sensor readings - it's a must, you're shooting in the dark without it.

Free Scan tool TunerPro and TunerPro RT - Professional Automobile Tuning Software

Here is a link for detailed TPS adjustment info:
Adjusting the TPS
Click to expand...
 
1bad89

1bad89

Active Member
#9
#9
Our cars usually run rough at idle when they're cold. Try adjusting TPS setting. But like Robert Lee said a scanmaster is essential to these cars. That's odd it does it when it's only hot, so if you replaced all of the above, and made all the adjustments. Could very well be a sensor. O2, ect. I would try a turbo tweak chip with closed-loop at idol. Worked for me. Good luck !
 
Guss23

Guss23

Active Member
#10
#10
When it starts and it’s cold it starts out at around 15 to 1800 RPM and as it warms up the idol drops down to where it should be but then it starts acting up.
 
1bad89

1bad89

Active Member
#11
#11
Sounds like a vacuum line . Could even be a check valve in one of the vacuum lines itself. But if you don't have a scan master, it's going to be a hard one to find. you should really buy a scanmaster and fine tune the motor. That's my opinion as a first step in the right direction.
 
Guss23

Guss23

Active Member
#12
#12
I do have a Scanmaster I bought a few years ago. I’ll get it out and see if it I can trace anything down. Is there a good reference to factory settings?
 
8289ta

8289ta

Silver Member
#14
#14
I had a crappy idle and hard start issue until I set the TPS and IAC/throttle stop. My car idles at 825 in gear when warm now. Check out the TurboBuick sites about how to set them. It may be worth a shot.

Check out all the vacuum lines and it might be worth just changing them for the heck of it. Especially, make sure all the lines going to the wastegate and solenoid are intact. A problem there can be catastrophic.

Check out this thread to get an idea of how to set TPS and IAC
How exactly do adjust the iac
 
Guss23

Guss23

Active Member
#15
#15
OK, I hooked the scan tool up and there was nothing crazily out of wack. I have replaced the IAC valve and O2 sensor. I adjusted the TPS at idle and WOT. I am changing the fuel filter, readjusting the IAC and installing a new MAP sensor tonight. I have sprayed down all vacuum lines with starting fluid as well as the throttle body area and intake manifold with starting fluid and found no leaks. I am going to buy a fuel pressure gage this weekend and check overall fuel pressure. WHAT HAVE I MISSED??
 
R

robert lee

Gold Member
#16
#16
Your changing the Map or Maf ? You really need a smoke machine to check for leaks, check the plastic vac. block on the TB, change the fuel filter and post the SM numbers after it warms up, Btw, how old is your battery?
 
R

robert lee

Gold Member
#20
#20
Just checking (bat), it could still be the Maf, parts house replacements are junk. you will have to get a Lt-1 maf and a translator, even if its not bad now its just a matter of time, like i said before change the fuel filter and post the SM after it has warmed up.. also if you have a stock chip you need to remove it and throw it as far as you can, replace with Turbo Tweak...
 
Guss23

Guss23

Active Member
#21
#21
I installed a new MAF sensor and the car started but immediately died. Started it again and again, immediately died. Did this 8 or 10 times and then switched it back. Went back to Oriellys and got another one and it did the exact same thing. Is there another procedure? It does have a stock chip.
 
Guss23

Guss23

Active Member
#24
#24
Don't know if this has to do with my problem but I discovered a minor vacuum leak in the hose going to the brake booster on the booster side. When I removed the line I noticed it had a strong smell of gas in it. I put a hose clamp on the booster side. At idle I did notice a variation of rpm when I pushed on the brakes. The brakes work fine so it is not affecting the functionality of the booster but maybe its an issue with the booster
 
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