After warming up my 350 tpi runs rough. It idles rough and accelerates almost like it's got a dead cylinder. It also smells lean. Oxygen sensor shows lean as well. All of the cylinders are firing, though. When hooking up a scanner to it, it's like none of the sensors are reading correctly. Half of the time the scanner can't even get useful data from it(or all the time if you call zero tps movement and incorrect readings useless). We've tried replacing the computer, chip, maf sensor & relays, ignition module/coil, spark plugs, oxygen sensor. Fuel pressure is good. The scanner never shows it going into closed loop, but I can't really be sure since all of the readings are bad.

The car runs badly not when the engine is warmed up, but when it is itself warm. Either a couple minutes after starting on a cool morning, or immediately after sitting in the hot sun. This makes me think something under the hood is getting hot and not doing its job. With this problem also came a ticking noise when I accelerate(or just rev the engine). It's not an exhaust leak or a lifter or valve. It's a ticking noise that sounds like it's coming from inside the dash, I haven't checked for it inside the engine bay when running.

We've replaced almost everything. The engine has only 8,000 miles on it. I was guessing that the EST module since that's about the only thing I haven't replaced, and its in the location that the ticking sound originates. Out of ideas.

 

Sounds like an Ignition component getting hot and not doing its job. My guess would be EST or Module.

 

If you check the base timing with a light, you should see a difference in advance when the EST is in bypass mode or active. That may give you a clue about the ESC.

 

Thanks Vader, I was wondering about that. I'll check it out as soon as I get back home.

I was considering just buying a new EST module and putting it in, but if it doesn't fix the problem that's a loss of $90. Who'd have thought it would be so expensive.

 

I borrowed a known good EST module and it didn't fix the problem. I did notice a hissing sound under the engine bay, kind of like a vacuum leak. However I couldn't find any in the runners, egr valve, or any of the vacuum lines. I think it may just be the sound of air coming in through the hollowed out plenum/runners.

My only idea now is a problem with the distributor. Most everything else checks out. The distributor is a 2 year old msd unit, the cap and rotor are new. The car does seem to start a bit harder than before, but that may be unrelated.

 

Check your grounds lately?

 

I had the EXACT same problem.....check ALL of your runner bolts and EVERY bolt on the intake itself....I had about 10 vacuum leaks from the runners and the PCV system was clogged. I took the plenum and runners off, took the vacuum hookups that screw into the plenum off and re-sealed them with Permatex thread sealant......along with ALL the runner bolts. The piece for the PCV system that screws into the intake manifold was so loose when I put a wrench on it, it fell out.....check that stuff...and replace ALL vacuum lines...good luck

 

I fixed the running rough problems, it turns out that my 1500 degree wire insulators were insulating the heat inside them, and 1/3 of my wires were melted just a little. Replaced them and the roughness went away, but a new problem arose.(I also fixed the vacuum leak, turns out a hose off on the side near the fuel pump relay had broken, didn't effect running but made a huge hissing sound).

When the car is in gear now, it will shudder for half a second. Rarely it will backfire through the exhaust when it does this. It's not like anything I've felt before. My friend says it feels like a valve is hitting a piston, but I don't think there is any chance of that since the timing hasn't moved in a year and it's always been fine. The engine hasn't ever been raced. It revs smoothly, but when driving on the street it seems to hit a wall at 3000rpms and not want to do anything until it shifts. Nothing was touched today except the spark plug wires and the ESC module(see last post).

Clueless. Haven't checked the grounds, do I still have reason to?

 

Might be a good idea to reset the ECM now. Grounds are probably okay, but don't take a lot to verify.

 

Been reset. I just checked and the grounds are fine.