Well, I still haven't torn in to my condenser fan problem, and now THIS comes along... <img src="/forums/images/graemlins/confused.gif" alt="" />

My '95 SR 3.5 DOHC has decided it does not want to idle any more. Well, almost.

If I release the throttle, the engine will "de-rev" straight down to zero, with only the slightest hesitation around 600-700 RPM.

If I gradually let off the throttle, once it gets down below 400 RPM or so.. it will level out, and stay there, or maybe even climb to 500 or so.

If I start it, without any accelerator pedal, it fires right up and dies. If I hold the throttle a bit, it will fire and jump up to 1000 RPM (or wherever I have the throttle).

Same behavior, hot or cold. Was already 100 miles in to this tank of gas. Cutout is not "sharp" as normallay associated with ignition issues. No misses or rough running at higher RPM's.

Thoughts:

1) Plugged fuel filter? - Dunno when it was last changed.

2) Fuel pump going bad? - Are these rigs mechanical or electric?

3) Idle controller? - I assume these rigs have an electronic idle control on the throttle body to go along with the electronic injection. I unplugged the connector immediately below the air inlet to the throttle body, as it looks suspiciously like an idle control motor. No change in idle when I did that.

4) Injectors? - Thinking a can of cleaner couldn't hurt.

I'll start hunting thru the FSM first chance I get (figures I'm out of town this weekend <img src="/forums/images/graemlins/angry.gif" alt="" /> ). If anybody else has some ideas, I'm happy to hear them. I've looked here thru some of the "idle" threads, but so far haven't found anythng that matches my model.

Thanks.

when was the last time it was tuned up? and btw, if i didnt know the last time that the fuel filter was changed... that would be first on my hit list. good luck.

My first guess would be ISC (Idle Speed Control) Servo. Not sure where it is on the 3.5 but on the 3.0 SOHC it's right next to the air intake (4:00 position) on the engine throttle body. It simply needs to be removed and cleaned with a lint free rag.

Also remove the intake hose (may be easier to access the ISC when you do this) and clean (using a rag w/out solvents & don't use carb cleaner) the inside of the throttle body as far as you can reach.

Ray <img src="/forums/images/graemlins/kewl.gif" alt="" />

Look under IAC or ISC in the FAQ. There are lot's of threads about it. Here is a link to another site regarding the IAC.

IAC ISC data

Off-Roader; Another question. Why do you say not to use carb cleaner when cleaning the IAC? I always take mine off then spray throttle body cleaner through the passages.

Thanks for the feedback, gentlemen. Just got back in to town, and will have opportuntity to look at this tomorrow.

Responses aqnd further Q's-

Grass13:
I don't know about the last tune up. I did my valve seals about 3K miles ago, and did spark plugs/wires/PCV-valve then. I didn't do fuel filter, or anything inside the throttle body.

(Actually, I don't even recall seeing the fuel filter. I looked in my owners manual when I took a brief look at the rig last week, and it doesn't indicate where it's at. I'll have to find it in the FSM. Anybody care to ahsre how much of a PITA it is to replace?)

Off-Roader:
Thanks for the info. I suspect that's the module I umplugged above, as the descriptiption/location sounds similar for my 3,5 DOHC. Perhaps that's why unpluggin it made no change.. it's sticking. That also may explain why for one start/run sequence everything seemed to work fine. Potentially good news that it can be cleaned, rather than having to be replaced.

Winston:
Thank you for the links.. I'll be doing some reading.

I just did my fuel filter three days ago. It's on the crossmember behind the transmission next to the driver's side frame. It has two 12mm bolts holding the bracket to the crossmember, and a 10mm bolt holding the filter in the bracket. The fitting on the incoming line uses a 17mm wrench and the outlet fitting takes a 19mm wrench. I actually used a 5/8" and 3/4" for them. Overall took me about 10 minutes. <img src="/forums/images/graemlins/cheers.gif" alt="" />

I've been giving this advice a lot lately, but... If you've recently disconnected the battery for any extended period of time the ECU may have 'forgotten' the idle settings. To see if this is the problem, I would completely disconnect the battery & let it sit for a minute. Then, hook the battery back up & start the truck w/o giving it any gas if you can. It should be able to idle now BUT you need to let it just sit & run for at least 10 minutes without messing with the throttle.

HTH,

Shawn

SRMan-

Thanks for the heads-up about the filter.


Shamer-

Interesting. The original behavior was out of the blue, no battery disconnect condiiton. Now it so happens that the rig was sitting over the weekend with the dome light on, so the battery went completely dead. Since then it has exhibeted the behavior intermittantly.

However, i puled the IAC, and one of the 4 windings is reading ~1600 ohms (it should read 30). I went ahead and cleaned it up anyway, and reinstalled it. It still idles eratically at times, and other times completely dies.

Given that the one winding appears to be shot, I think I'll give a rebuilt one from http://www.crebotech.com a try, rather than spending $250 for one.

-Steve

Well, now it won't die at all.

Seeing as how I've gotten practice "feathering the throttle" when it misbehaves, I think I'll drive it like ths a bit longer.

Perhaps it's the fuel filter after all... but I still have 1600 ohms on one of the 4 windings of the IAC.

Hmm....

Yeah, that dead winding will occasionally cause the motor to stick, messing up the idle. When mine did that, switching off then restarting would usually reset it. Usually...
and other times it will be fine. If it were mine, I'd just fix it...
Toby