Rough idle, engine miss at medium throttle

I have owned my truck for 12 years. This my third engine and I have been chasing down this problem all the while. Despite different engines (new ones) there has always been a skip/miss at all speeds. It runs good and gets 20 mpg. But I just cant seem to find the problem. This new engine from Jasper was installed with all new stuff and it still does it! I suspect it may be an issue with the HEI system (fine tuning or upgrading), a timing issue or maybe its just typical of this engine. If so are there any changes, upgrades or fine tuning that can be done to remmedy this issue. I am a pefectionist when it comes to my ride so please help this is driving me crazy. PS- Ive been through about 4 exhaust manifolds over the years. Why do they keep cracking?

Have you checked the MAP sensor, EGR valve and EGR contoller?

Never replaced the MAP sensor (not sure how to check it), EGR replaced with new engine, not sure about the EGR controller

Ill try that. What is the correct gasket? Thanks man

My workhorse truck finally left me on the side of the road after 15 years. The power steering pump bracket broke in half - belt came off. Drove the truck back home without the belt - replaced the pump bracket and replaced the serpentine belt. Now the truck wont start. Barely turns over, runs rough and makes terrible noise for 30 seconds - then upon trying to restart. Nothing. Runs fine without the serpentine belt - but when installed - wont run. Is the timing belt maybe out of sync when the pump bracket broke? Worked fine - now cant drive it with the belt on. Thanks for any help.

Ill try that. What is the correct gasket? Thanks man[/quote:fe1452c045]

Check to make sure none of the pullys on the belt drive are locked up. The 4.3 has chain driven timing, and that has nothing to do with the accessory belt anyways. I get the feeling one of the accessories locked up: the belt drive does have the ability to keep the motor from turning in these trucks.

My S10 Blazer has intermittently developed a rough idle that sometimes clears up after running the engine at high revs for a bit. Seems worse with cold weather. Engine trouble code is 33. Have already replaced the MAP sensor, seemed to fix, but problem came back.

With colder weather now, it is constantly in rough idle. Will stall if left at idle. If throttle is opened wide, engine will run fine until gas pedal released and goes back to idle.

1. I am trying to find the ECM module to see if there is a connection problem in it - web says it is located under glove box, is this right?

2. Any other ideas as to what the problem might be as it is not a faulty ECM.

Thanks

Ok, will do that- where is the ecm module located? The web pages indicate it is behind the glove box, but I have partially disassembled the dash, and I don't see it yet.

Hi, my pickup that is having rough idling issues and hesitation while accelerating. The problems only occur after the truck has warmed up and the acceleration issue only happens when I try to quickly accelerate. I am also noticing a decline in fuel economy as well as an increase in the smelly of my exhaust. I have pulled a spark plug thinking that they might be fouled or just gaped improperly but they looked fine.

I have a blazer and it was doing kinda the same thing. Get it warm and see if there is a knocking in the distributor cap. That should help narrow u down a little. I got a rebuilt distributor and new plugs and wires the truck runs great!

My 89 Chevy S-10 has 71,000 miles.
The engine runs good when it is cold, but
when the engine warms up it seems that the idle lowers and the engine starts to run rougher than when I first start it up.
The engine begines to run so rough that it acts like it's going to stall but does'nt. I've replaced the Air idle controll valve, new ECM, new plugs and wires and an O2 sensor. The EGR valve seems to be OK. I've had a vacuum check done on the valve (EGR) and it seems to be operating properly, but i'm unsure if it could be bad. When I hook up a vacuum gauge to it the idle does change. If I do it while it is could it starts to run as it would when it warms up. What would be the problem is there something that I might be over looking? What might the problem be?
PLEASE HELP!

Ive Checked the EGR valve to see if there was any carbon build up. The area where the EGR valve seats seems to be fine. I don't see a whole lot of build up.
I've checked all the vacuum lines to see if they were plugged. They seem to be clear. I've also checked all the vacuum inlets going into the throttle body for any heavy build up. I found that the line for the PCV valve had some heavy build up, but was able to clean it out with some throttle body cleaner.? Would a worn pcv valve cause this problem. The reason i'm asking is because when I pull lose the pcv valve line off the throttle body the idle seems to smooth out quite a bit and the idle comes up just a hair. How would I know if the electronic vacuum sensor is working properly?
I've taken some throttle body cleaner and sprayed the surrounding areas of the EGR valve really good and also cleaned inside where the valve sits. The inside of the throttle body behind the EGR valve did'nt appear to have alot of carbon- just minor amounts. I sprayed throttle body cleaner into this area just incase there was. I also sprayed the area around where the injectors spray and around the IAC
valve and just about any where else I thought that minght be effecting the vacuum air flow. It's still idling rough when its warm but seems to be trying to run a little better that's why I was asking if the pcv valve might have a part in this. That's why I'm also asking about the electronic vacuum sensor. You pull the vaccum lines off and I've got vacuum on one side but not the other. Oh! The egr valve does seem to be moving fine but, it does make a slight rubbing sound.
I'm working at it little by little but, I know that the issue will be terminated eventually.