Ok, here's a weird problem for y'all. About once every 6 months, my truck ('87 22R carbed) will idle rough. It misses badly, sputters, and the idle rpms will go up and down repeatedly, from about 800rpm to very low, almost killing the engine. However, I can still make it home because the engine runs much better while accelerating or at higher rpms.

The last time this happened, I let the truck sit for about 10 mins, then pumped the gas pedal once, and it started up and idled perfectly. So, I'm thinking it might be the choke sticking or something else, I'm not exactly sure. It's hard to describe/fix because I can't replicate the problem. Oh well. Any advice would be appreciated. The truck has had new plugs/wires/cap/rotor/fuel filter/fuel pump/pcv/air filter etc within the last 6 months.

 

im having a really bad rough idle too.. and whatever anybody says... check your TPS before buying a new one... there may not be anything wrong with it.

 

Does sound like poss. EGR, have you checked it's operation? But, maybe the TPS or throttle valve limiter. Simple vacuum leak, small one, could be too.

 

Forgive my ignorance, but does the carbed engine even have a TPS?

 

Good call, nix my TPS advice. Timing?

 

I've pretty much ruled out timing and ignition because it will only run rough very rarely. If I understand the EGR system correctly, it only functions at idle and low rpms? That might explain it...

 

Check the secondary throttle plate sometimes they will get very carboned up and hang ope just a little bit. I check them with a long thin screw driver while it is running and idling rough tap on the throttle plate to close it all the way. If it does close then a carb. o/h is in order.