Intermittent Idle Fluctuations AND Random Stumbling

aontkos

aontkos

New member
Happy New Year!

I've been attempting to diagnose some intermittent issues with no luck. So far I've had no CEL and no pending codes, so it's been difficult to find the cause.

Most of the time when my truck is in drive but idling my RPMs are 590-610. Occasionally, I'll notice increased vibration and see that the RPMs have dropped to ~540 but will return to normal within a second. This is without the A/C on, so it's not the compressor kicking on. The truck doesn't stall, but I don't think the RPM drop is normal since it didn't do this when I bought it.

I've also had rare instances of power loss while accelerating and maintaining my speed. It almost feels like the engine isn't getting fuel for a split second, but the stumbling doesn't last long enough for me reference my RPMs or voltage. This has only happened 2-3 times in the last 2 years, so I've just written it off as "bad" gas, but I'm also concerned that it may be related to my idle issue.

Any insight is appreciated!
 
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LittleCaesar said:
Thoroughly clean the throttle body and IAC. Also clean the MAF.
Click to expand...

I cleaned the MAF about three weeks ago and have gotten the symptoms since. Throttle body was cleaned ~2 years ago during a valve cover gasket replacement and still looks clean. IAC was also replaced at that time.

Maybe a TPS issue?
 
aontkos said:
I cleaned the MAF about three weeks ago and have gotten the symptoms since. Throttle body was cleaned ~2 years ago during a valve cover gasket replacement and still looks clean. IAC was also replaced at that time.

Maybe a TPS issue?
Click to expand...

Had exactly the same type of mystery intermittent miss on my 2000 carried on for a couple of years but was so random I wasn't too worried about it. Turned out to be the TPS.

It finally got regular enough to predict when it would happen (as soon as engine reached operating temperature, usually 2-3 miles driving).

I have one of those cheap ebay bluetooth code readers and the Torque pro app. Put up a TPS sensor graph and went for a drive. The graph should be a straight line on normal driving. The miss happened and the graph shows a sharp downward spike. Bingo, finally got the annoying bugger.

(Great way to nail it down for sure, bluetooth readers are less than $10 and the app was about $6, highly recommended.)

Replaced the TPS, miss is totally gone, slight performance improvement noted as well. Cleaned the IAC while I was at it and the idle fluctuations are also gone.

Also replaced the two mounting screws with M4-70 x 10 allen head cap screws, (Same ones that fit the MAF)

Gary
 
aontkos said:
Happy New Year!

I've been attempting to diagnose some intermittent issues with no luck. So far I've had no CEL and no pending codes, so it's been difficult to find the cause.

Most of the time when my truck is in drive but idling my RPMs are 590-610. Occasionally, I'll notice increased vibration and see that the RPMs have dropped to ~540 but will return to normal within a second. This is without the A/C on, so it's not the compressor kicking on. The truck doesn't stall, but I don't think the RPM drop is normal since it didn't do this when I bought it.

I've also had rare instances of power loss while accelerating and maintaining my speed. It almost feels like the engine isn't getting fuel for a split second, but the stumbling doesn't last long enough for me reference my RPMs or voltage. This has only happened 2-3 times in the last 2 years, so I've just written it off as "bad" gas, but I'm also concerned that it may be related to my idle issue.

Any insight is appreciated!
Click to expand...

Definitely sounds like the TPS. If you replace it - replace with Toyota OE. Had the same symptoms before and the replacement of the TPS kicked it in the butt. Good luck.
 
me too, years back
Similar symptoms, no codes stumble at a certain RPM. Did not have the torque app at the time ( do now, recommend). Cleaned everything. My wife ( x now) volvo had a similar issue and it was the TPS, (very expensive on a volvo)
the OEM ones for Toyota are not that expensive and I thought, I would gamble.

Problem gone
 
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