Ok, I've got this odd problem that only seems to occur when there are passengers in my truck. Sometimes its bad, sometimes not so bad.

Anyway, yesterday and friend and I were going to pick up a friend. I was going about 70-75 on the highway (which is normal), and then I got off. We were sitting at a red light at the off ramp and my truck's idle starting jumping around and getting very low (below 500 RPM, it normally idles from around 600-700 RPM).

The idle became extremely rough, and then the light turned green. Step on the gas and it hesitates slightly but drives fine to the next light. This time, as Im coming to a stop, I see my tach go from about 1000 RPM to below 500 then back again, and it starts idling rough again.

Light turns green, drives fine all the way to my friends house (about 5 minutes later, and 1 stop light).

This problem seems to only occur when other people are in my truck. Otherwise it idles pretty smooth, no problems, etc.
Later today I will try going to AutoZone and seeing if maybe there is a misfire code...but until then, Im wondering if someone else has any ideas?

I've cleaned my IAC (back in march or april though). Could bad spark plugs cause this? I have about 114k on the odometer and I bought the truck with 96k, I dont know if the plugs have ever been changed or not.

Thanks.

BTW the CEL never came on...

 

Johngs,

The symptoms sure point to IAC problems. If the DTCs don't point to other problems, I'd try a NEW IAC. I've read on these boards that cleaning the IAC is a temporary fix at best.

Good Luck,

Bill

 

Actually, I was thinking EGR. long highway drive will hold it open and allow exhaust to go through ( which is how it is supposed to work) then you get off the throttle and idle up to a stop and the egr hangs up a little, causing a lean mixture and a lean misfire. Might try the old EGR and port cleaning. Iac probs usally cause low idle or stalling, they don't have much to do with mixture control and haven't heard of them causing roughness.

 

Well tomorrow I am going to go to AutoZone and I'll have them scan it and buy an oil filter since Im due for an oil change.

 

I had neglected my maintenance as I do alot of idling. My plugs tend to foul, and then I glaze them buy accelerating too hard after work.

I changed the oil/filter, pcv valve, cleaned IAC valve, and put in new plugs and air filter.

Ran well for me after. I eventually had my DPFE go on me, causing hesitation and loss of power. After replacing that, everything went back to normal.

 

Johngs,

Can you give us an update? Did you get the codes read @ Autozone. Did you fix the problem? What was the cause?

TIA,

Bill

 

I'd like to hear an update on this one too, because this is the same exact symptoms I am seeing - intermittently. So far, I have done the following to address this problem:
Replaced the plugs (in March)
Cleaned injectors (in March)
Replaced EGR and DPFE (in March)
Cleaned the IAC (last month)
...then replaced the IAC (3 weeks ago)
Cleaned the MAF and TB (last week)
Reset the PCM (last week)
Replaced the PCV and hose (last week)

But, the problem still remains... Still only happens when fully warmed up, and sitting at idle in gear for more than a few minutes (long traffic lights, etc)

Next on my list to try is:
Clean EGR ports
Throttle Position Sensor
Replace upstream O2 sensors

Mine is a '98 with the 5.4L, with 86K miles....

I am certainly open to ideas, advice, etc. H E L P