89 5.7L

Hi guys, I have an 89 vette tpi 5.7L yesterday during a cruise it started idiling quite high, about 1700 to 2000 rpm. Does anyone have any ideas where I should start looking?
TIA
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Maybe the fuel injection system?!
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Mike Radlin wrote:

Apologies for this being so long. Here's the way I'd tackle it:
You don't say how stable the idle RPM is, or if this is a manual or automatic car. If automatic, it's worthwhile to know if the rpm is the same in Park or Neutral. If different in park and neutral, skip to using the scan device and check out the 'P/N' self test. Also, does it attempt to run at 1700 rpm in Drive or, in first gear if this is a manual.
Sounds like too much air. Rule #1 on this is, aside from the throttle position sensor, don't adjust anything or throw any parts at the problem until all the diagnostics have been run. (You can quickly go through a couple of hundred bucks in bits and pieces and not find the problem.)
First, make sure the electrical harness and connectors on the Idle Air Control and Throttle position sensor are OK. Both are on the right side of the throttle body. The sealed adjustment on the IAC isn't used to set idle rpm -- leave it alone.
Second, dump the stored codes from the ECM. (paper clip across terminals A & B on the diagnostic socket, ignition on, engine not running, etc.etc.) If there are codes write them down then disconnect the negative terminal from the battery for 15 minutes to 'zero-out' the ECM. Then reconnect the battery and go for a 'training drive.' Training drive is in the shop manual. IIRC, 5-10 minutes of idle, some highway cruise with easy part throttle accels and decels. Look for engine check lite etc. Bring it home, shut down, start it, check idle. Shut it down and write down any codes. see: << http://corvettebuyers.com/ecm4.html
Third, inspect vacuum lines everywhere. Hunt for a vacuum leaks. Brake booster has caused idle problems for some -- 17 years, maybe it's time.
Fourth, open up the inlet and see that the throttle is closing all the way. Look for dirt or a piece of gasket that might have fallen down into the idle air passageway, wedging the idle air control valve open.
If all of that looks OK and there are no codes, find someone with a shop manual (section 6E3), a scan device and the software to read out a 1227165 model ECM (a notebook computer, ALDL adapter cable and software like 'Freescan v2.0 or v2.01' by Whittaker will do this job.) << http://www.andywhittaker.com/ecu/ecu_software.htm
The scan device will show what the IAC is doing, help in calibration of the throttle position sensor and show a couple dozen other readings.
Note: There is a sealed adjustment screw on the IAC. Don't let anyone turn it unless you are ready to spend $ 85 for a new one.
Best of luck.
-- PJ '89 Hookercar '02 e-blu coupe
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Thanks PJ!

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Damn, sorry I forgot. It's an automatic and idle is stable both in park and neutral.

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Looks like the P/N logic is OK. It's time to work through the troubleshooting chart in the shop manual. Please let us know what the problem finally was.
Mike Radlin wrote:

--
PJ
89 HookerCar, 02 E-blu 6-spd Coupe
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Actually, it turned out to be the throttle position sensor, the first time i checked it it seemed ok, but the second time it wasn't. Thanks for all the help!

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Cool and glad it worked out OK.
PJ
Mike Radlin wrote:

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