High idle, codes 41, 91

June 27, 2015, 04:33:13 PM

This is on my 100% stock 91 Lincoln Mark VII. The car has had a high idle in park (900rpm). I ran KOER codes and got 41 and 91 (system lean right and left). I've done the following to trouble shoot:

Remove all vacuum lines from intake except fpr and PCV. Checked engine vacuum and it was 18" at 900rpm idle (idle still high). KOER codes were 41, 91, 33 (emissions systems disconnected for test as I was trying to eliminate vacuum line leaks as an issue).

Re-connect all vacuum lines. Engine vacuum is still 18" at a 900rpm idle. KOER codes 41 and 91.

Checked fuel pressure. 30 psi engine running vacuum line on. 39 psi engine running vacuum line off. Within spec.

HEGO ground wire is still attached to intake manifold.

None of this has obviously pointed to a problem. I doubt the car has a intake/massive vacuum leak as it makes 18" of vacuum at a 900rpm idle speed. I also doubt both HEGO sensors ped the bed at the same time. Is there anything else to check besides probing the HEGO harness with a multi meter? If that turns up negative any ideas on what else could be the issue? As a FYI what ever is causing this will trip the check engine light after about 15 minutes of driving. This just started happening on it's own. I have done nothing to the car prior to the issue appearing.

High idle, codes 41, 91

Reply #1 – June 27, 2015, 04:54:37 PM

Verify the TPS doesn't have a issue... If it were mass air I'd tell you to clean the MAF meter, but SD I dunno, possibly the MAP sensor is beginning to fail?

High idle, codes 41, 91

Reply #2 – June 27, 2015, 05:30:29 PM

Fixed it already. The HEGO ground that I thought was connected to the engine wasn't. I touched it and the wire fell off the lug. I attached the ground wire to a new lug and then reattached the wire to the engine. Idle went back to normal and I ran another KOER test. Got a code 11 for system pass. Easy fix this time.