Slight stumble at 6.25 rpm (1 Viewer)

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I have been doing lots of reading along with the fsm and can't figure this out. When the cruiser is idling it goes from 6.25 rpm and drops to 5.5 rpm(than catches and bumps back to 6.25). Also occasionly drops down to 3. Prior to this I had a code 71 but resolved the problem. The wires, plugs, cap, rotor, fuel filter, belts have 15k on them--all oem straight from Dan. I checked the resistence on the wires and all are with in factory spec. I also pulled all the plugs--a couple have a brown tint on the top white part but aren't really fouled. The air intake hose is new. I have pulled the plugs 2x with no change. I'm starting to think fuel injection. Also if I put my hand close to the exhaust it surges like it is missing. Any other ideas?


The cruiser has about 147k with all pm done at 132k except for the phh.
 

desmocruiser

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Had a similar post a couple of weeks back. I have also changed the fuel reg, 1 fuel injector (the cyl that would occasional misfire according to cel), tps, egr valve without any change. With the help of several members I am very suspect of the engine wiring harness (slight damage by the egr valve and inside cab by glovebox brace as well as having to extend the wires for the trd s/c). The wiring harness is going in next week, I'll keep you posted. In the interim you may check out my previous post under strange idle some good advice by other members on that and others.
 
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Sr. Gringo, you might want to try a GOOD injector cleaner, even a couple rounds of it in your gas, and if that doesn't take care of it, clean the throttle plate. When I first bought the 80 I noticed a very slight stumble at idle. I ran two bottles of Redline fuel treatment with only a half tank of gas consecutively, and it took care of it. IMO very nice product, have used it on all my vehicles.
 
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desmocruiser said:
Thanks. I haven't quite figured that one out yet.

Don't bother with the regular search. Go to the advanced search page and you can do all sorts of cool stuff. One of the easiest is to put yourself into the "search by user name" field and then pull up all your own threads/posts. Kind of interesting to look back and think "Did I say that?" :D

Curtis
 

powderpig

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Try checking the throttle Position sensor, If out of adjustment. either clean the throttle plate, then check the TPS. Or jsut adjust the TPS with knowing the plate may be dirty and need cleaning. After this check the timing. If the TPS does not registar that the Throttle plate is in idle mode, Idle will be all over the place. Good luck robbie
 
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One thing I didn’t mention is I live in Mexico and the gas down here is awfull…..gas station tanks have lots of sand and silt in them. I’m going to try changing out the fuel filter tomorrow, and a shop is going to clean the injectors tomorrow. I have run 3 bottles of the chevron injector cleaner over the past month with no change. Right now there is no cel and never has been other than for code 71 which is now fixed. My harness looks good behind the egr valve but I will try that if all else fails. The egr passes the fsm test. I haven’t checked the tps yet—something to try for tonight. Also as Dan mentions in the thread above my throttle cable is real ugly on the outside maybe time for a new one. Also going to pull the glove box tonight and look for shorts. I should also mention the air flow meter was just replaced with one out of a used cruiser. All these problems started when I decided to wash the mud off my motor—big mistake don’t do it! Also when I replaced the air flow meter the truck didn’t start until I pulled a spark plug wire. My problem sounds exactly like desmocruiser’s—please keep me updated as to what happens. I will do the same if I figure out a solution. Thanks all for the help. This is a great board.;)

Where is the tps located? My fsm is at home right now.....
 
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powderpig

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It is on the front of the throttle body. It is the one with a 4 wire connector, not the motor. opposite of the throttle cable and the kick down cable, and the crusie control cable. good luck robbie
 
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powderpig said:
Try checking the throttle Position sensor, If out of adjustment. either clean the throttle plate, then check the TPS. Or jsut adjust the TPS with knowing the plate may be dirty and need cleaning. After this check the timing. If the TPS does not registar that the Throttle plate is in idle mode, Idle will be all over the place. Good luck robbie


Robbie,

I cleaned the throttle plate and took apart the tps. Everything was pretty clean--now its shiny... Everything is smoother now but the problem is if you cup your hand behind the tail pipe there is a pulsating...poof--poof--poof--poof. I will take out the glove box tonight to look for shorts--can you suggest anything else?

Thanks,


Jason
 
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I'm thinking it's an O2 sensor. Mine was doing something similar, and after cleaning the throttle body and doing a tune-up didn't fix it, changing the O2 sensors did. I did have very sluggish throttle response as well.

I don't know if there's a diagnostic to test them, but my CEL wasn't on either for a long time, but when it did finally come on, it threw the O2 sensor code.

Something to consider.

Ary
 

powderpig

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So you hooked a Volt Ohm meter to the 4 pins inside the TPS and measured the resistance and got the values it required in the FSM? Then did you check timing with the proper pins in the diagnosistic cocnnector? If so your problem is some where else. Try doing the check in the FSM for the Idle air control motor. That may lead you to your problem. later robbie
 
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powderpig said:
So you hooked a Volt Ohm meter to the 4 pins inside the TPS and measured the resistance and got the values it required in the FSM? Then did you check timing with the proper pins in the diagnosistic cocnnector? If so your problem is some where else. Try doing the check in the FSM for the Idle air control motor. That may lead you to your problem. later robbie


Robbie--you did great. Looks like the tps is the culprit. The values are bad according to the fsm. I got the stuttering fixed with new plugs and a new gas filter--was really plugged after 1 year. One thing that showed up is code 71....... So right now my truck idles at 450 w/ the A/C on--you have to remember to pump the brakes....


I have the new egr modulator for 50k and it appears to be o.k.
There really isn’t any excess carbon build up that I can find
I am thinking of purchasing a temperature sensor, and vsv—I figure by the time I’m able to remove the vsv I may as well put a new one back. Any other suggestions?

My truck is also missing the orange/black check valve—is this essential?
 

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