Hey guys. I posted a while ago that my 99 Jimmy 4X4 4.3 had some major electrical issues. Im pleased to say that I finally fixed the tps circuit and elimated other electrical problems too, however, my jimmy still suffers the same symptoms.
When cold, it runs pretty well. When revving it, it has a small stumble but picks up after a split second. And driving down the highway, it runs great, but it starts to run horrible when it gets up to normal operating temp.
When the jimmy is hot, it has a very rough and erratic idle, and when you rev it, it stumbles for about a second, then starts to pick up again. It seems the more throttle you give it, the worse it gets. Also, i dont know if this is normal, but as soon as the throttle blade opens, the intake sucks in alot of air. If i put my hand over it, it will suck my hand to the maf and compress the intake tube, but just for a second. It seems like its trying to take in alot of air.
If your on the highway when its hot, it seems to stumble under light throttle, and if you mash it down, it starts to miss horribly with a dramtic loss of power. Sometime it will misfire in the drivers side header. fuel milage is also abismal.
I have no dtcs other than p0300. Anyone know if this could be a vacuum leak? Electrical seems to check out as I had to check everything to figure out earlier problems. Any help or input would be greatly apprciated.

 

Was your distributor removed recently?
I had a similar problem, caused by inserting the distributor off by one tooth.

 

Well at first you said that it runs good when you first start it up, then you said it starts to act up once it warms up and P300 is a random misfire. I would have a compression test done after you check every sparkplug and its wire. Then if all thats good, check the gapping on every plug or even replace them thats what? 12 bucks. At this point you'll know you have spark, Now you need to know if you got gas so do a feul pressure test, this cost nothing at pep boys fyi.And this is why I tell you this its because once the motor gets hot the feul pump,internal rings and and only a few more parts break down only once it gets hot. And that feul pump can cause a random misfire.

 

Man disregard my last post you know what this sounds like to me sounds like your cat is clogged up man think about it put your hand over the exhaust if its barly coming out thats your problem even better drive it at night then look under in if its glowing red or you hear atig tig tig noise right after you turn it off thats exactly what it is. but if your cat has already been cut out then dont disregard my last then lol. Just trying to help but this has happened to me before and if it is the cat it will get worse