I tuned up old faithful about a week ago and it was running like a really noisy watch; somethings changed. Around town it seems fine, but after a highway drive I get blips of the check engine light and when I slow down I get a series of surges (about eight) until it settles out at the normal rpm. The code indicates O2 sensor. That's brand new so I'm not inclined to think it's the problem. No loss in power or mileage. Valves were adjusted. Timing seems right on 12 degrees BTC. Vac hoses and gaskets seem tight. It's acting like it's hunting for the right mix of air-fuel. Also deceleration is extreme. Almost like a jake brake effect. Any ideas? I keep going back to the timing, but advancing or retarding it gives me pinging or sluggish acceleration. Would a faulty throttle position sensor cause this?

Check your cat. converter. If your exhaust braking seems out of line and you are getting an o2 sensor light maybe the o2 is flagging because it's not getting enough flow across it because of the clogged converter.

Just a thought.

I doubt it's the tps. You'd have drivability problems around town as well.

'Not the cat converter. It was brain lapse on my part. I'm my own worst enemy. When I did my tune up I took off the throttle body to clear the carbon and gum out of it and loosened the throttle position sensor to work the throttle plates. I didn't have to. I shouldn't have, but I did it anyway. To compound the problem I put it back together and forgot to tighted the screws so it seems the TPS gradually worked it's way loose. I didn't mark it's position before I fooled with it so I had to guess about where it was originally. Well, to make a long story short I turned it back to the position where the engine picked up a bit and wonder of wonders the surging and jake brake effect stopped. Of course now I'm thinking there is probably a way to set these things with a voltmeter instead of the ol' eyeball and ear technique. Any threads out there that might give me the method?

If no one replies before I get home, the Haynes manual has a procedure for setting it. I'll post it when I get home. About an hour or so from now, give or take 30 min.

I just took a look at my Helm. There are 3 terminals for the connector on the sensor. They line up vertically and are respectively refered to as:

| I
| P
| F



hth
<img src="/forums/images/graemlins/cheers.gif" alt="" />