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Please HELP, sporadic idle after new mani install

5298 Views 63 Replies 14 Participants Last post by  Tred
Im out of ideas, and so are a few people from this forum that have been helping me. I'm hoping some bright minds out there have a few more ideas. Upon cold start, the rpms at idle start at 2 and slowly rise until it warms up. Once warm, its a sporadically jumping idle between 1k and 3k, but is usually bouncing between 1.5k and a bit over 2k rpms. It is like your very consistently reving your truck. Also if i let the rpms drop below 2k while driving and I'm in gear, the car will accellerate until that threshold of that "sporadic idle"

Steps i've taken so far:
- Searched high and low for vacuum leaks
- Replaced the Throttle Position Sensor
- Cleaned Idle Air Control Valve
- Cleaned MAF
- Reset the ecu
- Plugged in my laptop to make sure something isnt weird with the map on the tuned piggyback

The truck has NEVER done anything like this before. I took it to santos' place and all he did was put on a new manifold (very pretty one i might add). Since i drove it home from his place is when it started doing it.

WhAt ThE FvCk could be causing this!?!?!? :mad: :confused: :( :rolleyes: :runaway: :eyecrazy: :puke: :cry:
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After consulting with a few people, some were convinced this was the problem, after replacing it and still having the same problem i know its not this...


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in case ur wondering what kind of dumba$$ idle my truck has, here's a video
check all gaskets like the tb gasket or the intake manifold gaskets they can leak and cause a weird idle
tb gasket was replaced today, intake mani will be next...
no other ideas?
What exact sort of 'manifold' was installed just before this started up? :thinking:

What were your idle speeds (cold and warm) before this started?
Check for intake leaks using brake cleaner. Sounds like you've got a high idle and the ecu is cutting fuel when it "drops."
the new mani is one of santos' new log style turbo manifolds. my old one was cracking and falling apart. that plus i converted from internal wg to an external tial 38mm.

95trokita and i tried the carb cleaner test already with no luck. however the high idle with fuel cut description makes plenty of sense. on cold starts it idles waaay high, and then after it warms up is when the bouncing of the rpms and revving starts happening.

normally before the issue, on cold starts it used to sit at about 2k to 2200 rpms, and then once it warmed up it drops to between 500 and 800 rpms.
After it warms up, unplug the front oxygen sensor. See if the bouncing stops and the high idle starts again.
A strange idle speed can be caused by a short or no signal from the air conditioner (yes - A/C ...) control switch. If the ECM 'thinks' the A/C is engaged when it isn't it can result in high idle speeds.
interesting, well how would you go about checking that a/c control switch and determining if thats a possible culprit?
Turn it on and observe for changes in RPM.
... Or remove the 10A AC fuse, re-start the engine, and see if anything changes.
Turn it on and observe for changes in RPM.
lol well turning on the ac always had an effect on the rpms at idle, but not this drastically so i think i know what you mean... and this gives me one more thing to check, thanks guys.
Dam Mike always something, Have you disconnected the IAC when running and observe RPM?

Check AC like stated above as well.

Do you have a CEL??
Dam Mike always something, Have you disconnected the IAC when running and observe RPM?

Check AC like stated above as well.

Do you have a CEL??
x2 in the IAC disconnection. I've been seeing a lot of taco IAC's dying lately for some reason, check the resistance of the coils in the IAC valve.
Check the iac my truck did this bought a new a/c board and tested wires ended up bein iac valve did change ur tb by chance 00-04 will make that happen on 95-99
of course its always something lately, i cant even believe it myself though. this put me over the edge, im not buying anything more for my truck before i buy a dd. thats it. anyways, i even tore all the ic and piping off tonight and bypassed the turbo completely to make sure it wasnt that. its not a/c and its not an o2 sensor.

i guess cleaning iac wasnt enough, but someone has to explain to me wtf this thing actually does and how youd disconnect it. theres been some controversy with a few people over what to replace. with the tb off i was looking at 2 coolant lines and a gasketless peice of metal that openly connected through to the tb. there was another sensor plug that runs lower than the tsb cable plug and pulling that thing doesnt do anything either. and as far as internally, my methanol has proved to really clean the insides nice, the tb and intake mani are flawless lol.
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