940 Idle misfire, very light throttle misfire - only when warmed up

'91 940 turbo, essentially stock except for Shane's fuel chip. It has a cold start injector. I have a copy of the LH2.4 greenbook and a meter, but haven't gone digging because I'm low on time, so I turn to you fine folks for a gentle nudge in the right direction so I can go from there.

Cold idle/driving is fine, and warm idle is fine for a little while; it consistently acts snotty only after sitting warm for a while, with stuff under hood heat soaked. At throttle tip-in, sometimes misfires a bunch, sometimes not, more throttle clears it up, runs fine on the highway. Grounds all pass the jiggle test (will check them all with a meter). Slight gas odor at the FPR.


Will check for obvious large vacuum leaks, TPS function with a meter, the usual ignition suspects before I check back in here.

Do you have a wideband? Are you seeing anything there?

Have you made any recent changes? What do plugs look like?

With heat soak electronics can get flaky. Like the ignition amp on the inner fender or the engine speed sensor and air mass sensor. I've had the ignition amp cause a stall and no start for awhile till it cools off. But that would only happen after about 20-30 minutes of driving.

Belated update: naturally, it hasn't done it again. However, I checked all the basics, and did find plug #2 is missing its little thread-on nubby . So I'll go ahead and do plugs/wires/dist. cap since that plug wire boot was a little toasted on the inside from all the arcing, and go from there. Also replaced the intercooler hot side S-shaped hose, since it was very soft.

Only time it acts snotty now is when it's been raining a boat load and it sits for a while. Can the AMM act funky if there's a lot of moisture in the air, i.e. if the wire burn-off function isn't doing its job? Idle is great, cruise is great, only stumbles at the poke of the throttle. Once warm, no issues.

FWIW, it may not be directly related to your issue, but while you're in there I'd pull the powerstage, separate it from the heat sink, clean and reapply some thermal paste between the two to prevent the issues that dl242gt mentioned.