My truck has very recently started misbehaving. It's a 2001, 5.9L 4x4.

When I start the truck... idle will bounce between 700 and 1200-1500 rpms when in neutral or park, at a cadence of about one second. The range is less if it is in gear with my foot on the brake. It seems to do this all the time... warm, cold, it doesn't matter.

I think the surging happens all the time, but I just don't notice it as much when it is in gear and driving down the road. I cannot feel the surge when driving for the most part. I think the "load" seems to absorb Sometimes I notice it when stopping, it feels like it is getting some gas. The tach reports about 1000 RPM as I am slowing down/stopped. When I come to a complete stop, the tach eventually settles back down to 6/700, and you can see it kind of bounce between to the speeds at the same cadence. If I let off the gas, and shift it into neutral as I am coasting to a stop light, it will also bounce between 700 & 12-1500 RPMs.

I do not have a check engine light on, and I have not checked for codes yet either. I probably should do that though.

I tried using the search tool on this forum... but the search tool appears to be totally broke. Using Google to search this specific domain only seems to work so-so.

I'm hoping that this is a simple TPS replacement, and/or perhaps an IAV replacement.

I don't think it is the fuel pump, because it is never starved, but rather getting excess gas.

Does anyone have any recommendations on what to check, and which order I should go about replacing items? I would prefer to change things one at a time until it is resolved because (1) I'm a cheap bastard, and (2) it can help someone else out in the future with a similar problem.

I seem to recall some TPS check/adjustment procedures at one point... but with the search not working, I can't find it.

Thanks,
Cartman

 

TPS, or possible vacuum leak.

TPS voltage should be right around 1 volt, or less... with the throttle closed, sweeping SMOOTHLY up to greater than 3.5 at WOT. Best to check with an analog meter, as the digital guys don't really react fast enough. (testing is done on the signal return wire to the PCM, don't know just off hand which one that would be on your truck.)

Do your vents work right? 4x4? if either/both don't work as they should, start looking for a vacuum leak.

 

4x4 and vents do seem to work. Only under heavy load uphill do my vents drop out. They are fine all the other times.

I had a rotten EVAP canister hose that I had to replace last year, so it is possible that other vacuum lines are brittle. Since my vents seem to be functional (for the most part), I am hesitant to think this is exactly what is causing it. I don't recall other folks posting about wild vents reporting this kind of behavior. But... I probably need to check those at some point.

I'll try and test TPS tonight when I get home. It looks like the control wire is in the middle...

Thanks,
Cartman

 

This thread kind of died. I have the same issue. Mine doesn't ALWAYS do it, though. My truck surges when cold (cold start, ambient temps are over 100 right now) for awhile after start. In the video it surged for about 30 seconds to less than a minute (total, not all on video) then completely stopped.
Sometimes it surges when idling in park and warmed. But not always.
Sometimes it was also idle up and stay there. I was waiting at a parking lot for someone in park and the idle speed went up to around 1900RPM and held there perfectly for awhile.
My cruise control and 4x4 both work, so I assume there is not vacuum leak, or a small one. I'll connect a vacuum gauge tomorrow and see if that shows anything useful. There are so many vacuum lines I'm not even sure where to look to get all of them.

Anyway, here's a video shortly after cranking. The surge is just as the OP described: idle speed up to around 1500RPM, back down, surge up, down, etc. Then it completely stopped at 0:20 during the video.

 

my 99 1500 4x4 is doing the same thing rpm from 600-2000 at idle hot or cold and my vent go to defrost on engine load . i have a factory service manual cant find any info on the vaccum reservoir. cruise is affected as well it drops speed and picks it back up on load loss which is kind of nice instead of kicking down on the least little hill like it used to. I wanna fix the problem though!!!!!!!!!!!!

 

I'd say all you need to know is in this thread, https://dodgeforum.com/forum/2nd-gen...ild-vents.html

 

i would agree ! thanks