TPITuned Port Injection discussion and questions. LB9 and L98 tech, porting, tuning, and bolt-on aftermarket products.
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Hi everyone, been lurking around this site for a while and decided to post my problem and see if I can get some good info. I have a 92 rs B4C w/350 TPI. The car has been sitting for 4+ years and I have just recently been trying to get it back to being a reliable car. So far I have had to replace the fuel pump and the IAC valve. My problem is now I have a very high idle that I cannot get to go down. I have reset the IAC as per the article in the Technical section here on the sight to no avail. Still I have a very high idle. I have checked all hoses for the possibility of a vacuum leak and everything looks good. I know the IAC is functional because I cranked the car with the IAC out and watched the Pintle move back and forth. I am running out of ideas. Could this be caused by a faulty Throttle Position Sensor? Maybe a faulty ECM. Any help would be greatly appreciated.
Thanks
John
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Last edited by Brad8k; 10-21-2009 at 02:00 PM.
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yes the tps can do that. that is actually something i woulda went after before i checked and replace the iac. take a voltmeter (unless u have access to a scanner) and check for .54 volts at idle.
Your IAC works in conjunction with your Coolant Temp Sensor, and if the CTS is bad (no reading), the ECM will assume a cold engine throughout, thus keeping your RPM higher. 2500-RPM is up there though, so other than your CTS, I would hit the throttle body linkage with some WD-40 (more than likely binding due to sitting so long). Also, you want to be checking for a vacuum leak by the china wall (where the intake ports meet the cylinder heads), and while your at it, check your power brake vacuum line....
.... your TPS is reading that high at idle? Did you have the same problem when you parked the car in the first place, or was it idling okay? Unless someone intentionally moved it while it just sat around, yes, it is way too high.
Edit: Again, if it is non-adjustable, then check your throttle linkage, it sounds like it's binding.
Street Lethal-No, it never idled that high when I parked it and nobody has been under the hood but me. I will check the throttle linkage and post back. Thanks
.... your TPS is reading that high at idle? Did you have the same problem when you parked the car in the first place, or was it idling okay? Unless someone intentionally moved it while it just sat around, yes, it is way too high.
Edit: Again, if it is non-adjustable, then check your throttle linkage, it sounds like it's binding.
Does your throttle butterfly shaft go all the way back to the throttle stop?
Also, your TPS voltage is too high for idle. Speed density TPS should be somewhere between 0.7 and .9v at idle and go over 5 volts at WOT. Voltage progression should occur in a linearly progressive manner with throttle applications.
The best way to tell is not by extending the throttle to see how far she'll go, you need to soak the linkage wire with WD-40, then blip the throttle linkage very fast (while idling) with your hand. Open and close the flap as fast as you can, just to see if the idle settles at a much lower RPM. If it doesn't, and continues to remain that high, your TPS is more than likely shot. In Open Loop, the ECM bases fuel requirements on the location of the TPS, it has a preconfigured look up table, and since the reading is that high, the ECM assumes it's at part throttle and is adding fuel. Once the engine goes into Closed Loop, it will start to surge, because the O2 will try to correct, and thus the game of tug of war will begin. Long story short, if its not the linkage, its more than likely a bad TPS (common)....
Street Lethal-That is what I was leaning towards is a bad TPS. Thank you for explaining how the ECM relies on the TPS, that kind of narrowed it down for me. However I think I will look deeper into the throttle linkage before I get another TPS. Thanks for the help!
Seriously, you should change the title of this thread and add [FIXED] to it so that people searching know their was an actual resolution to this one. Congrats!
I had a problem alot like that in my89 tbi what I found was the base gasket under the tbi had blown and the computer comp by adding more fuel so the car wouldn't run lean .The car would idle at 1300rpms, Hope this helps
