Missing at idle only 88 5.7 k1500

[dirkhood]

I need your guys help again with my 88. On and off again I have had issues with missing, I change something, it gets better, then it comes back. Last time it was the spark plug wires. The time before it was the distributor cap. This time it is only missing (sputtering) at idle. If you even give it a little gas, it runs great.

The truck got a bad miss full time and I ended up taking it into the shop. I found out the #2 cylinder spark plug wire was shot. I just changed them 100 miles ago so still under warranty. To be safe, I put in new AC plugs, changed the ignition control module, dist cap, rotor and ignition coil. The MAP sensor was changed out a few miles back. It still misses at idle but runs like a new truck when you touch the gas. I checked the egr valve and cleaned it. I also visually checked for any vacuum leaks in the lines.

I'm now at a loss, what would make it miss at idle, both in park and at a stop sign? It seems to get worse when it is warmed up. I appreciate in advance any help you can provide.

[procaddytech]

Sounds like a possible O2 sensor stuck lean or rich at idle causing the ecm to richen or lean the fuel mixture excessively. Very possible vacuum leak or worn distributor shaft. Carbon buildup maybe. Have you tried Top Engine Cleaner or Seafoam? With it worse when warm points to too much fuel. The O2 may not be swinging high when idling. With a single wire O2, you can back probe the connector with pos. lead of meter and ground the neg. lead with O2 still plugged in. Set the meter to millivolts and see if O2 swings well above and below 450mV after warmed up and in closed loop. Check for full engine vacuum at map sensor. Low vacuum will cause higher fuel delivery. Just a few thoughts. Good luck.

[Schurkey]

PCV system OK? Doesn't pull excessive air through the valve?

TPS voltage at idle is correct?

[dirkhood]

I changed the O2 sensor as I had purchased one a while back, no difference. TPS might be it, I move it ahead a bit and it appears to stop the popping coming from the passenger side of the engine. How can you test if it is the TPS sensor going out? Are their other sensors it might be?

[dirkhood]

Pulled the PCV valve out and found out it was the end of a air hose nipple. Why do I always get stuck with someone's half witted attempts to fix things. New PCV valve and it ran like a champ. Thanks

[broughy84]

Another thing to check even though you have your problem solved is the fuel spray. Make sure the spray from the injectors are conical and without drips. When I had a stumble at idle in my old 88 that's what it was. A quick rebuild and all was better.

[j cAT]

Originally Posted by dirkhood

Pulled the PCV valve out and found out it was the end of a air hose nipple. Why do I always get stuck with someone's half witted attempts to fix things. New PCV valve and it ran like a champ. Thanks

on a 1988 engine the PCV needs replacing every 30-40,ooo mi with normal driving..stop/go driving more often. some THINK THAT THESE FAIL WHEN THE GET PLUGGED UP....THE real problem with a well cared for engine is these valves no longer work as designed and wear out ...this causes idle issues and may cause higher oil use ....premature engine wear.

if the engine is properly maintained the PCV will never get plugged up....