So I bought this car a few weeks ago and it had a high idle problem (2300-2500 rpmand race rich as hell. Today I replaced all the vacuum hoses and adjusted the TPS back to 0.54. That lowered the idle speed down to 1000 but according to my scanner, the ecm keeps switching back and forth between open and closed loop mode with is pushing the rpm back to 1300-1500 rpm.

I'm thinking I have a couple of things going on here put it don't want to just start throwing parts at a problem. What's the best way to test the IAC's and o2 sensors on these things? I'm not getting a CEL any longer and it's not running rich any longer. Any help would be great! Thanks!

 

anybody?

 

that idle speed is still a little high(actually about right if engine still cold)Could check the CTS as the original style with concentric plug can develop a bad connection and give false temp reading to ECM.Is engine getting up to normal operating temp-~195*?-some here have reported engine staying in open loop if coolant temp too low,but my '82 C/F seems to switch to closed loop as soon as O2 sensor warms up and outputs voltage to ECM regardless of coolant temp.You can watch the IAC pintles operate by looking down the IAC inlet ports as throttle is worked-they should move the same distance at the same time-if they are out of sync,they should reset if car driven.Also check over the "lid"gasket for vacume leaks or loose bolts.

 

All of the sensors on the car are at least 30 years old and the ALDL diagnostics are not very robust to say the least. I replaced the CTS, MAP sensor, O2 sensor, the ECM as it was the wrong replacement number and all the vacuum lines around the cruise control unit and mine idles perfectly. None of the sensors were throwing a code, but I replaced them anyway. It really isn't that expensive.

If you haven't replaced or checked the vacuum lines around the cruise unit up by the radiator area, I would definitely check that out. Another thing is to make sure the manifold bolts are torqued correctly.

Hope that helps some.

 

Yes, very big deal on a CFI.

 

I'll check the CTS tomorrow just to be sure. The MT2500 was reporting 93C(forgot to change it) which I believe is around 200F. My problem isn't that its staying in open loop but its literally switching back and forth between open and closed loop within about a second which is causing a "loopy" idle. By "lid" gasket are you talking about the air cleaner?

I've checked and replaced all the vacuum lines under the hood. Including a line that was missing from the fuel tank pressure control valve as well as a rotten plug on the PCV. I will check the intake manifold bolts as well tomorrow. Anybody have the torque specs?

Will definitely check them. Does anybody have a recommendation on a service manual so I can have these kind of specs handy?

 

"lid"is the plate on top of the manifold that the TBIs are mounted to.If the scan tool was reporting 200*coolant temp,sounds like your CTS is good and the coolant temp correct.CFIs are picky about fuel pressure-too low will cause unstable idle speed.

 

Ok thanks for the clarification. As soon as I replace the front wheel bearings in the old lady's escalade I'll start working on this...then again I found a local third gen collector selling/trading parts and I might have to spend some time with him today