89 Town Car CEL & code 34

[Mark2fish]

I have an 89 TC w/43k original miles. Bought it six years ago at 28k. I'm hoping someone has experienced the problem I am having. I get a CEL intermittently acompanied by what seems to be en excessive advance in ignition timing. Soon the engine will run at fast idle around 1400RPM. Shutting the ignition off, then restarting will cure the problem for a day to a month. I had a code 34 with KOEO. I replaced the EGR valve and EGR position sensor, replaced all of the vacuum lines in the EGR sytem, and replaced the EVR filter. I verified EGR operation by observing EGR open and close after stabbing the throttle. (It did not seem to be operating this way prior to my servicing.) I was able to pop the hood during one of the fast idle episodes and observed that the BPA had an excessive drive voltage. The throttle position sensor checks OK (checked several times). Any clues anyone?

[87 town]

I have an 89 TC w/43k original miles. Bought it six years ago at 28k. I'm hoping someone has experienced the problem I am having. I get a CEL intermittently acompanied by what seems to be en excessive advance in ignition timing. Soon the engine will run at fast idle around 1400RPM. Shutting the ignition off, then restarting will cure the problem for a day to a month. I had a code 34 with KOEO. I replaced the EGR valve and EGR position sensor, replaced all of the vacuum lines in the EGR sytem, and replaced the EVR filter. I verified EGR operation by observing EGR open and close after stabbing the throttle. (It did not seem to be operating this way prior to my servicing.) I was able to pop the hood during one of the fast idle episodes and observed that the BPA had an excessive drive voltage. The throttle position sensor checks OK (checked several times). Any clues anyone?

My first thought is the Idle Control Motor. If not working right it can push the idle up too high or even too low. I had similar issue in the past. It is the silver cylinder part sitting next to the the driver side firewall. Motor can get stuck now and then. "Maybe" this is what is happenning? You can unlplug the wire connector on it to test it and watch for changes in idle.
This seems to be a bit of a common problem. Mine cost approx. $70 a couple years ago and was a real easy install.
P.S. I'm not suggesting you throw this part at the problem, and I don't understand most codes... Just going off the logic that too high of an idle could be originated from to a bad ICM.

[Mark2fish]

Thanks '87 town" for the consideration and reply. I think I might have inadvertantly solved the problem when I left the hood up and the engine compartment light ran the battery down since I dont recall having cleared the code register after sevicing the EGR system. Since I only have 20 miles since EGR servicing and 10 miles since the hard reset (battery < 5volts), it may take a few weeks before I know if the problem is cured.

[gadget73]

Ah, if you didn't reset the ECM after fixing the problem, then it will take a bit of time to re-learn in order to properly asses it. The seeming excessive timing advance is usually what is observed when the EGR doesn't open. The exhaust gas slows combustion and allows the use of more timing. Without the exhaust flow, the car tends to ping and may randomly buck and carry on while driving at part throttle.