intermittent idle misfires
 

Curious problem of intermittent misfiring at idle speed. Operating temp or cold doesn't affect it. Holding 2000 RPM (with difficulty) for about 1 minute clears it and then it idles fine and runs well at highway speed. Wide open throttle will also clear it, but not good to run it to 5000 rpm with 250,000 miles. OBD II error codes show multiple misfires, O2 sensor, but these are thought to be secondary to too much fuel when problem occurs. Has anyone seen this before?

atleast put down year make model

intermittent misfires
 

Oops! Yes, that might help. i'm new on the forum. It is a 2000 Suburban 1500 with a 5.3 LS 1. Hope you can help me.

Hi I am in the same trouble with the same kind of car. 2000 sub 1500 LT with. 5.3l . misfire on cylinder 4 . and o2 trouble code. the misfire intermittent and both code disappear and comes up together.
O2 code comes up because the missfire . you have to focus on the misfire. multiple misfire is worse then the located misfire because hard to find which cylinders misfiring..
my oppinion you have to start with sparkplugs and coils gasoline filter . check the cylinder compression if it is ok intake leak also can causing misfire . with your mileage time to take the intake clean if necessary , new gasket ,new knock sensors and new cranckshaft position sensor .any of these can causing the misfire. even injectors can be the problem . start with the easiest and do it step by step. i am still working on mine I will post is if I find my solution. If you have the diagnostic tool better if you post the freeze frame data too.

2000 Chevrolet suburban 1500, 5.3 liter. Thanks for your thoughts. The fuel pump and fuel filter were replaced one year and about 20,000 miles ago, along with knock sensors. OBD II consistent code (after erasure of all codes) is catalyst on Bank 2. As you recommend, I will approach the problem one step at a time. A vacuum leak was considered because the old cars, before computers, could sometimes develop idle roughness. I remember one on which the throttle plate shaft was worn and allowed air entry. Throttle body on this engine seems solid and the misfire is not consistent. I will post as progress is made. New cats and O2 sensors tomorrow. Thanks again.

update on 2000 Suburban 1500 5.3 liter intermittent idle misfires
 

On my way to have the catalytic converters and O2 sensors replaced on my 2000 Suburban 1500, 5.3 liter, it really acted up. To the point that I did not think the misfires would clear or that it would have enough power to make it to the shop, but it finally did. Cats and 4 sensors replaced and it has not misfired since. About 1000 miles on it now with multiple stops while at operating temp and many cold starts. The check engine light had been on for a long time, but codes were erased from time to time to see if the same code or codes were consistent. As written in a previous post, the catalytic converter on bank 2 has been underperforming consistently. stored codes were read at the time of repairs: PO 154: O2 sensor, no activity bank 2; PO 300: random/multiple cylinder misfires (no surprise there); PO 430: Catalyst below threshold bank 2; and finally, PO 440: Evap emission control inoperative. I will replace the evap control tomorrow, along with new spark plugs which have approximately 100,000 miles on them. Plug wires are also being replaced since they are original equipment--17 years and 252,000 miles. These were not causing the misfires, because it runs fine now.
After erasing the codes, none have come back, so the major problem apparently started as a worn out catalytic converter on bank 2, followed by a failed O2 sensor. Of note is the exhaust odor is much cleaner since new cats were installed. Theories abound as to why the engine would misfire at low RPM, then clear when held at 2000 to 2500 RPM for a little while. After reviewing a few YouTube videos on the subject, I now believe it was due to no fuel trim on bank 2 at idle speed, then bank 1 trim carried all injectors at higher RPM. Hope this helps someone else with a similar problem

alright so you have the same problem i have on the same thing, 200 sub 1500, but mine has 297k miles. ive been dealing with this crap for a few months, luckily only city driving to and from work, no highway. until today my truck had no balls and would do what yours is doing but only after its warmed up.

i changed the spark plugs and wires today. holy. crap. i think i have the wrong wires as there is no slack in the wire but the spark plugs OH MAN they were BAD. they looked like they havent been changed in 150k or more miles. i ran into a problem with mine though, some idiot cross threaded the drivers side plug closest to the bumper (forget which cylinder that is), and someone drilled out the hole in the block and used a helix ring. when i took the plug out the ring stayed on the plug, not to mention the old wire got stuck on the plug and broke while removing it. it took a lot of liquid wrench and pb blaster but i got the helix ring off and put it on the new plug and it went in just fine. that spark plug was completely different than the other 7, which leads me to believe the helix thing came off on at least 2 or 3 plug changes prior to me and rather than fix it the right way they mustve used the same plug over and over.

this might be your problem too, im not sure, but it worked for me with pretty much the same symptoms. apparently there are 2 different kinds of plug wires for this, one has an angled boot and one is straight. the angled ones were on before so i bought those and while they are on snug and secure i dont trust it because the wire itself is kinda taught; im thinking its supposed to have the straight boot ones as they might be slightly longer.

on a side note, when i pulled the messed up spark plug out i was beyond pissed off, and i evened up my drivers side fender with a nice fist dent so it kinda matches the passenger side now. tomorrow is brakes day though so yay!

2000 Suburban 1500, 5.3 liter with 252,000 miles. Original problem was intermittent idle misfires. OBDII did not identify cylinders other than "multiple misfires." Spark plugs and plug wires replaced about 500 miles ago, along with the fuel vapor control valve on top of the intake. Some of the plugs had heavy deposits, but none of those interfered with the spark gap. From the appearance of the plugs, all cylinders appeared to be receiving adequate and even fuel. There have still been no misfires since replacing O2 sensors and catalytic converters 1500 miles ago. The check engine light has remained off. OBD II shows no codes. I believe the intermittent idle misfires were due to a worn out catalytic converter which may have damaged the downstream O2 sensor. At this point it runs well and fuel mileage has improved about 1-2 mpg when compared with old records at interstate speeds of 65 mph.
Signing off for now. Thanks to those who replied.

if its misfiring at idle the intake manifold gaskets are probably leaking and causing a lean misfire condition. the condition corrects itself at 2000rpm because manifold pressure has increased and no false air is skewing the maf

Chevrolet Suburban 1500 5.3 liter with 252,000 miles: Thanks, Tech2: Good to know for future reference. This has been a curious problem from the beginning, but replacing the Cats and O2 sensors evidently cured it. If the misfires had occurred every time the engine was started or came back to idle, I could better understand the possibility of a vacuum leak, but it was irregular to say the least. Once cleared by holding 2000 to 2500 RPM for about 1 minute (with the exception of the time described above on my way to the repair shop), it would not misfire again until shut off and restarted, sometimes not even then.
There are multiple sensors giving feedback to the ECU these days that any one of them can disrupt full engine performance. Having written that, we are truly fortunate to have the performance and fuel economy of these computer controlled engines. I came of age in the 1960's when adjusting carburetors, spark gap, points and condensers, timing were our means of reaching peak performance. Simpler in some ways. Much different and better now. Cleaner air to boot.