Thread: A/F going very lean at cruise

Here lately when I am at a cruising speed, my a/f ratio will drop to 16.5 to 18.0. If I bump the pedal, they go back up to normal, but will just keep dropping to very lean conditions. Doesn't happen all the time, mostly when it's been cold in the morning. In the afternoon when I leave work, it only goes lean when I first accelerate, then the fuel will catch up. Once the engine warms up, it stops completely. Thought it may be the maf or possibly the tps, since I just repaired a weak connection at the maf harness. Checked the voltages on the tps and maf, but everything checked out with no dead spots. Just changed the fuel filter, so that's not it; plus it's getting plenty of fuel from the pump. Checked hoses and such for any sort of vac/boost leak. The only thing I haven't checked is the fpr. This only happens at cruise conditions, and is getting plenty of fuel at wot. I've kept the same tune with no changes for quite a while, and it's always been dead on.

Anyone have any ideas? Something I may be overlooking?

You have any CEL codes? For some reason I'm thinking your CTS might not be working properly.

No cel's. I figured the cts would cause it to run rich if it died, but for no more than they cost, I could give it a shot. The one in it is just a little over a year old. I did get it from Autozone though.

IT may not be dead, it may be giving false readings. Test it per the FSM's procedure, and get a trustworthy unit as well.

Thanks. I'll check it out tomorrow after work, and might as well place an order for an oem unit.