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General Tech Crazy idle/rev issue, at my wits' end....

Troop92

Troop92

Well-Known Member
Location
Layton, UT
Hi all. I have this up on planetisuzoo as well, figure more heads together... Fighting to track down an idle/rev issues that have been hounding me for months. It has become a big irritation.

In the morning I can start my Trooper when cold, he'll idle at 750rpm until he's warm and happy, and will keep idling like that. BUT, once I drive anywhere (even just around the block) the idle goes up to a jumpy 900-1100rpm, cycles up and down up and down. If I've been on the freeway and I exit and stop, it zooms up to 2500rpm, hangs there and eventually comes down to the 900-1100 cycle. It will NOT go back down to that low 750 idle until I shut him off, wait an hour or two, and start him again.

Cleaned: EGR, PCV, TB
Replaced: FPR, TPS and IAC (TPS/IAC a few months BEFORE symptoms)

I can't see any bad hoses for a vac leak, I sprayed TB cleaner all over the place and nothing changed. Any ideas? I can't figure why it'll idle perfectly at first startup and change so drastically when I drive it.

Thanks guys... Maybe you'll think of something that I haven't considered.
 
Rot Box

Rot Box

Diesel and Dust
Location
Smithfield Utah
I've seen Toyotas do similar things when the coolant temp sensor (for the fuel injection) goes bad. Fine when cold but once up to temp the computer still thinks the engine is cold.. Idle, timing etc go nuts. Something to look into anyway. Good luck,

Andrew
 
Troop92

Troop92

Well-Known Member
Location
Layton, UT
I'd seen mention of that a few times, but deep down I was hoping that wasn't it - since the CTS is on the back of the engine. You can go from below - if you lift the engine a bit, or from the top - if you take of the intake manifold... *sigh*

I'm hoping a vac leak, or something with the TB. I might just pull one this coming weekend from Tear-A-Part to put on whole and see what's what....
 
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Kevin B.

Kevin B.

Not often wrong. Never quite right.
Moderator
Location
Vehicular limbo
Any chance you can narrow the problem down a bit before going after it? You should be OBD1, have you looked for codes?
 
Troop92

Troop92

Well-Known Member
Location
Layton, UT
@ Kevin B. -- I don't have a CEL on or anything, but I guess it could be there without illuminating a light. I'll see what I pull tonight.
 
chans

chans

Registered User
Location
Sandy
Probably the dashpot. Googled it for Isuzus and looks like they have them. They get gummed up and stick or not return to normal position once you get some vacuum through it for a while. You can try pulling it off and try driving around and if no backfires than you are good.
 
Troop92

Troop92

Well-Known Member
Location
Layton, UT
Aren't dashpots normally found on carbeurated engines? Mine doesn't have one, it has an IAC that controls those functions, and I've replaced it a few times, thinking it was a bad one.... I doubt I've gotten that many bad in a row.
 
jeep-N-montero

jeep-N-montero

Formerly black_ZJ
Location
Bountiful
chans said:
Probably the dashpot. Googled it for Isuzus and looks like they have them. They get gummed up and stick or not return to normal position once you get some vacuum through it for a while. You can try pulling it off and try driving around and if no backfires than you are good.
Click to expand...

This is pretty common on them.
 
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