Runs rough untill warm 93 s10 blazer
 

Got a 93 s10 blazer vin w. replaced the intake manifold gaskets and heater core. and when i started it back up it runs rough when idleing. i have an after market air filter and usually if i unplug the battery and plug it back in. it would have to reset the air fuel mixture after a few minutes and it would be just fine and normalize. but now it wont untill it gets warm. when the engine gets warm it no longer runs rough. runs like a champ. when it runs rough it sounds like it sucks in more air at some points. and if i drive it right away before letting it warm up, i come to a stop and it would jerk me forward a little if i dont hold the brake down. it does not die on me though. whats causing this rough idle.

Ok think i found the problem. its the TPS sensor. throttle position sensor. and it does die on me now when i let it idle. sometimes it will sometimes not. Going to get the new sensor in the morning.

Now its it hard getting the thing started some times starts but then dies immediatly. but i got a used IAC idle air control and now it runs just fine. no problems now. no help needed lol.

I saw your post yesterday and thought you had it licked so I didn't respond. Glad you finally tracked it down.

Well i started her up this mornin and now it starting to act up again just as before. its surging at idle. and dies sometimes if you let it idle. ugh its starting to tick me off. replaced the tps sensor and idle air crontrol valve. i dont think i have a vacuum leak cause i can take a vac hose off 10 minutes after the engine is off and it hisses. what else could it be??? it just surges at idle but if you put the pedal down a bit it will be just fine. fine driving and everything. but not at idle. wants to die.

Taking a vacuum line off after the engine is shut down and hearing a hiss does not rule out a vacuum leak. The engine itself will not retain vacuum once shutoff. Only a running engine will produce vacuum. Chances are, you are disconnecting a line that has a check valve into it that is meant to retain vacuum.

If you can keep it running well enough, you can try to trace along all of the lines and the intake mating surfaces with an unlit propane torch to see if the idle speed changes.

Also a few things to check is wires and plugs. Had this happen to mines. Pop the hood at night with no light and look around the wires to see if there's arcing. A vacuum gauge hooked to a non ported vacuum port on the intake may give clues as to what's going on. You need to find out first if it's a vacuum, ignition, or fuel problem.

ok well i took it into a shop and had a mechanic take a look at it and he said he couldnt find anything wrong but said it might be the map sensor or egr valve so i said ok thanks and started my truck up and engine light came on instantly. but wasnt on before. so i went in and asked if he could scan the codes and he said the guy that had the computer just left and said to come back tomorrow. and he has the same blazer i do and i think he took some of my parts off and took his ****ty ones and put them on mine. wtf im never going to a shop ever again. ever. but what pisses me off is that i took it to advance auto and they ran the codes and it came out 32 and 34 egr and map sensor. go figure. wtf i just got ripped off big time. but i picked up a used egr valve and map sensor for 40 bucks so im going to put them on tomorrow. and if that dont work going to borrow a torch and find any leaks like you said.

You can test the map sensor yourself as well. I just posted a link to a thread where I ran down through the different altitudes and the base reading from the MAP.

alright i disconnected the battery and then put the egr valve on then the map sensor conected the battery back up and no engine light. it started no problems. a good minute later the engine started surging and idles rough again. i put some water and dish soap in a squirt bottle and went around the plunum and didnt seem to suck any of the water in or bubble up and no change in idle. so im at a complet loss right now. when its cold and starts surging and running rough i can put it into reverse or drive and it will smooth out and run just fine. but as soon as i put it back into park then it starts surging and rough idle. but i came up to a stop sign and when i made a complete stop it died but started back up just fine. so even though i didnt find any leaks with the squirt bottle i gave the plenum bolts another half turn and still didnt help. im going to get a torch and try that in a day or so when i get one any other ideas