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Discussion Starter #1 (Edited)
Hi everyone, long time reader 1st time poster. Actually signed up just because of this problem.
Its a pretty frustrating problem. You start the truck with no problem at all, the idle shoots up to about 2k as normal(cold) but as soon as it starts to warm up and drop the idle will suddenly shoot down to 600ish then rise to 1k then fall over and over. A look into the tb shows what seems to be both injectors firing full then cutting then full then cutting over and over.

My work horse, 1989 d21 with a vg30i. Truck has 220k miles on it, about 10k ago I swapped the motor with a 88z31 motor(70k) but retained the stock d21 electro injection. Eliminated the egr and pump, added headers. Ran like a dream for a few thousand miles then all of a sudden the surging idle problem developed. I ran the codes, det sensor, maf sensor, cas codes came up. To my knowledge (and all datas too) the truck never came with a knock sensor but I added one and the code went away, maybe I'm wrong Idk. I replaced the maf with a used one due to the cost and that code disappeared as well. Replaced the entire dizzy with a z31 dizzy using a d21 cap and that code disappeared. The surging idle did not though. I checked the tps with a spare I had, nothing. If you leave it disconected the idle shoots to about 2k and no surge. Checked timing with a light, on the money. I changed the IAC valves with one I had from the z31 plenum (All data says they run the same current) No change. The air filter is clean. There is a bit of a gas smell in the exhaust although no smoke so its hard to tell if its running rich and I should replace the fpr or not because the egr and pump are gone. I have run the codes a few times as well as disconnected the bat to reset the ecu. I get no codes(before the reset of course:)). I also tapped both injectors and checked the current, they seem fine. I checked all the vac lines and sprayed around the entire tops end with carb cleaner to see if there was a leak, nothing. I discovered while checking around with the ohmeter that the mixture heater is not working. There has always been a blown fuseable link (since I bought the truck)that I paid no mind since everything seems to work, all date shows that is the heater. In the last month or so I have changed the ignition module and alt as well.

The biggest lead on the prob I have to date is that I checked the chts resistance just to cross it off the list, it checked out and I said okay. Later that night I said well let me check the volts. Alldata calls for .1-.5 cold-hot, I assume thats a gradual change and as the voltage rises the idle will lower. When I checked it however I'm getting .1 .2 .3 .4 0, .1 .2 .3 .4 0 over and over in sync with the idle. So after that I took a trip to the junk yard and pulled a sensor of a van with a vg30e, I read its the same sensor maybe they are wrong but w/e the case when I plugged it in just to see if there was a change the idle shit to 2200 and the surge started again only now it was 2k-2.2k and the voltage too erratic to read. Idk what to think about that, or why the surge only happens after the truck begins to warm up. Does something over ride the chts when the engine is totally cold or for a certain time after start up? Could it be the chts and the one I got is just out of range? Idk, I am a decent mechanic but this has me totally stumped.

So thats where I am at. I am thinking fpr but at this point or chts, with all I have checked and been through I am asking for advice 1st. Just about had it to be honest, feels like maybe something stupid I'm missing.

I know there are many knowledgeable people here and someone is bound to help so thank you VERY MUCH in advance.

P.S. Sorry to ramble I just wanted to include everything I could think of to aid in diagnosis, thnx again.
 

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Discussion Starter #2
Not a single reply in 11 days? Maybe I should talk about turbos instead.

This forum is :lame:
 

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Dam i feel your pain, by know id imagine you fixed whatever the cause was? I would guess off rip something to do with cylinder coolant sensor or vacuum leaking ?
 

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Sup Mod keeping the peace
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You're replying to a 12 year old post. We as administrators try to discourage this type of action; it just adds to a lot of leftover trash. He's either probably fixed it by now or maybe sold the vehicle.
 

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Rogo man, 12yrs old indeed so why is that post still visible i understand what your saying but wouldn't reply to something thats not seen in current year form timeline dew to the age of post if it be removed or kept away from current forms when past a certain time period, actually it shouldn't even be visible on current forms at all but rather in archives or something. Cant honestly remember how i even stumbled upon it. But cool.
 
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