my 96 is a 4 cyl with 165K miles. after 45-60 minutes of hiway driving 70-75 mph with cruise engaged, a slight stall will occur that cannot be detected on the tach or speed then it immediately recovers and in 4-5 seconds will do it again. to stop it i disengage the cruise. there is no rhyme or reason when this happens. some days i can drive for hours and have not had it happen. but if it does, when i slow down to a stop or turn the idle will be a bit low and the engine usually will die. it starts right back up though. i have now founnd that this occurs with the cruise turned off as well and the stall is becoming more pronounced and shorter intervals (1-2 seconds) and now gas mileage is dropping significantly. i get no engine codes, have changed wires, cap, rotor twice to no avail. any ideas?

 

How is the cars acceleration, can you accelerate through the high-speed miss? The IAC valve controls engine idle speed, this would explain the dieing, low idle and engine being OK at restart.

 

I can accellerate (or decellerate) and the surging will stop. Sometimes I wonder if the problem is a bad spot on the throttle position indicator (code?) but I don't understand what that has to do with the idle problem. When it happens it feels a bit like when the egr valve is tested to see if the rpm drops when opened. Is the egr valve supposed to be closed in high speed cruise? Is it possible that the valve is cycling and causing the repeated stalls. But wouldn't that create a code?The cycling stall will continue until i either disengage the cruise or accell. I don't recall it ever stopping on it's own.

 

Well if you're cutting out at stops I'd do like toyomoho said, I has a similar issue with my 94 i4 and I cleaned out the iac valve, and it did help quite a bit. the iac valve takes in a certain amout of air when the throttle is closed (idle) and if there is a bunch of residue (like mine) blocking the iac valve then not enough air will get through to keep the engine going.

You'd be surprised how much can get past the air filter, all around my throttlebody and iac valve was completely stuck up and blackened with grime. After attacking it with the appropriate TB cleaner it was nice and shiny and clean again, you could hear the difference just aftercleaning it.

 

Thanks for the tips on the iac valve.
i removed it and t/b and there is some gumming of the passages. i checked the aic per alldata.com. the resistance is slightly out of tolerance on one side. both read 20.7 ohms, and the hot side should be 21.5 ohms. is that enough to be a problem? also applied voltage per test and valve does not close 100%, it appears to have a hard stop with the valve remaining open about .100". is this normal? replacement is $250 at autozone, want to make sure the valve is really bad before i replace it!!
pulled egr and it operates smoothly.
will the iac cause the high speed problem if gummed up?

 

Im not sure, but before replacing it, I'd say clean it. See what kinda difference you get with it clean. It only costs a couple bucks to get the tb cleaner from advance. Make sure its safe for sensors and plastics.

$2.50 as opposed to $250... I'd definitely clean it first.