Ok, so i got the mechanic to put in some new Knock sensors in my 93 Jimmy SLE 4x4, and it really helped the ide problem. But the idle still sputters, nearly dies and surges back to life. I even put in a new O2 sensor and had the injectors cleaned!

What am i missing? why does the truck always seem to want to die when idling? It runs strong, lots of power, good torque, great accelleration, but when im at a stop, especially when is cold it wants to die.



could it be the EGR valve? too much air? Vaccum leak?

Im pretty frustrated.....especially since im lucky if I get 200 miles to a tank >

 

Have you tested the fuel pressure and leak down rate?

 

Similar year to mines.... The thing about OBD1 is diagnostics, diagnostics, diagnostics. First try to pull any codes that will give clues as to what is going on. Second, do basic testing on components that are related to the symptoms. You will have to dig in there and really check stuff that will affect idle quality. If you don't have the tools, then you may want to find a better mechanic that is very familiar to Chevy OBD1 and knows how to look for it rather than throw parts.

 

No I havent had this tried yet. But now that you mention it, Ill look into it.

We just went down the the Oil Can Henrys to get an oil change and as we rolled out from the garage, the engine light came on....code 43, Knock sensors.....WE JUST REPLACED THOSE! So the guy said perhaps a bad CAM sensor is givng a false positive.....

Im getting sick of this. Whats a CAM sensor and whats the long term if i dont get it fixed right away?

Cana bad sensor cause poor gas economy, rough idle, and rattling engine on startup?

 

doubt it would be vacuum it would make the engine idle up. if it idles fine in park and dies in gear its possible. my buddy had a fullsize truck that was having a similar issue. if you tried to just give it a hair of gas to like maintain speed while driving it would die but idled and drove fine. took a while for me to find. ended up putting it in gear against a tree and saw that the egr valve was opening up all the way when put in gear and causing a huge vacuum leak

 

in park it idles and sometimes almost dies but then roars back up to normal idle, in gear it idles at a stopsign but also seems like its gonna die, sometimes it surges and a few times its almost surged away from me, I had to slam harder on the brake pedal to keep from rearending the car ahead.

 

I have a 91 and there isn't a cam sensor. If the knock sensor has set a code again you may want to check the wiring related to that or the sensor itself. The codes in OBD1 are general clues and unfortunately does not necessarily mean the actual sensor itself is the problem. The way other sensors affect each other it could be something else causing it.

The main components that will affect idle are IAC, ECTS, and EGR. May be a few others that I can not think of at this time. Don't go replacing these but test them to make sure they are operating properly. The IAC is known to get carbon build up on the pintle and port. Also the PCV port can build up quite a bit of gunk in their as well. If the engine coolant temp sensor is reading off then it could do this. Need a digital multi-meter to check it and associated wiring. The EGR could be sticking open a bit allowing flow @ idle which there should be none. It and the port may need cleaning. Another big carbon problem area.

Also check the Park Neutral switch on the lower steering column to make sure it's in the proper position. It is also used in the EGR circuit to help determine when to keep the it closed.

 

surging is usually EGR related....hopefully when the upper plenum was off to clean the injectors they changed the rotor and distributor. I just did this myself and since I was in there cleaned the crap out of my EGR one way you can check it's operation is to see if that pin that is spring loaded moves up and down freely when removed...just spray with carb cleaner...Then put it all back together but the same symptoms were still there... anyway I thought about the ignition coil replaced that and the car ran alot better but still not quite right...I then looked under the hood in total darkness and saw that my wires were arching or to me had lighting bolts shooting out!!! replaced my already new wires and now I get 18mpg city on a 94 s-10

 

I had the same issue. I replaced the knock sensor but the fault remained. I looked up my factory sevice manual and there are three components plus the wiring. The ECM-ESC-Knock sensor. Mine turned out to be the ESC-Electronic Spark Control box. It is mounted on the firewall. NAPA has new ones for around $80.00. I decided to try one from a U-Pull it junk yard. Less then $10 and 5 min. to change out in the junk yard parking lot and the fault corrected. If corecting the Knock sensor code does not correct your idle problem then you have all the usual suspects. IAC, TPS, Vacumn Leaks, Timing. Spark plug wire shorting out to ground. Good Luck See the link below for my original post.

https://blazerforum.com/forum/showthread.php?t=47914st.

 

try a full blown tune-up my idle problem had a lot to do with ignition wires that were only 6 months old replaced those and it idles and runs like a damn champ