# Idle stumbles when coming to a stop



## dongatta (Sep 29, 2008)

Hey all I have a 1986 D-21 with a FI 2.4L. When coming to a stop I push the clutch in and the idle drops like it wants to cut off then idles rough for a few seconds then back to normal. I have new 02 sensor coolant temp sensor thermo wax kit cleaned MAF ecu says throttle / idle switch. Went to the junk yard got a TPS and still same thing. Any help in the right direction would be greatly appreciated


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## brookwood61 (Aug 18, 2005)

Check your brake booster to see if it has a vacuum leak.Good Luck


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## dongatta (Sep 29, 2008)

New brake booster and master cylinder


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## zanegrey (Dec 5, 2005)

check all vacumn and check the bpt valve..it it the one right b4 the egr valve..

also check the fuel pressure regualator vacumn..some time moving it to a manifold source solves this prob..


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## dongatta (Sep 29, 2008)

Thanks for your reply.if you dont mind me asking what is the bpt valve and if you are facing the throttle body which side is it on.I have checked all vacuum lines numerous times.If i route the fuel pressure regulator to a manifold source what do I do with the ends that is coming out of the top of the throttle body going to the fuel pressure regulator.Again thanks for any help you offer.


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## zanegrey (Dec 5, 2005)

just in back of the tbi .. it almost looks like a flying saucer ..

cap it..


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## dongatta (Sep 29, 2008)

ok thanks what am i checking the bpt valve for and I will re-route the vacuum this evening and post back


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## zanegrey (Dec 5, 2005)

i am a little tired ...

so my first reponse to you should have been to try a tune up..

plugs wires cap and rotor fuel filter air filter and breather elemet.

even an oil change ...


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## dongatta (Sep 29, 2008)

Ok here is a list of all i have done thus far
Nissan Wires - NGK Plugs
Distributor - Cap - Rotor Button
Set Timing
Compression Test
Thermostat - Heater Core
Engine Coolant sensor - To the computer
New fuel filter
TBI cleaned
New TBI gaskets
FI filters & o-rings
Used TPS per Vehicle computer
What am I checking on the BTP


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## zanegrey (Dec 5, 2005)

check the bpt for operation.

with the truck running (you might have to idle it up for this ) 

pull the vacumn for the bpt ..note the effect..

put vacumn back on and pull the otherside vacum not e the effect ..and is the vacumn coming staight thru..

also check egr function..


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## dongatta (Sep 29, 2008)

Thanks I will check what you have listed and post back later on


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## dongatta (Sep 29, 2008)

Pulled vacuum on top of bpt engine ran rough pulled lower vacuum no effect. No difference when hooking up the fuel pressure regulator to manifold


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## zanegrey (Dec 5, 2005)

check the bat cables for looseness and or corrosion..

check all the way down to starter..

also check belts for looseness


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## dongatta (Sep 29, 2008)

Will do I am at my witts end on this truck


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## zanegrey (Dec 5, 2005)

you removed your old tps..??

how did you determine how to put it back on..??

what positon did you set it at.. ??
this might just be the tps is slightly out of line...


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## dongatta (Sep 29, 2008)

I just pulled it off the TBI and placed the other one on. I lined the old screw marks up on the one from the junk yard and tightrned it down


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## zanegrey (Dec 5, 2005)

you noticed it has oblong screw holes..

it can be adjusted..

there is a proceedure..but try lossenening the screws just enough so you can tap the tps toward the longer part of the oblong..

just a tap ..do not get crazy and move it too far..

then start and test its idle problem ..

do it a couple of times to see if it helps..


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## dongatta (Sep 29, 2008)

I want to say thanks for your time trying to help me get this truck rite. I had heard of a procedure of adjusting the TPS but I am far from a mechanic. I did notice the oblong screw holes. Should I take the TBI off to adjust the tPS or can it be done on the truck. There is only about a quarter inch adjustment either way correct.


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## zanegrey (Dec 5, 2005)

do not remove the tps ..

you only want it to move a fraction..

that is whay i saw to tap once retighten .check idle and then repeat if neccesary


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## dongatta (Sep 29, 2008)

Ok I will try when I get home. Truck is parked in the garage didn't drive today hoping to get the problem fixed. Post back later


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## dongatta (Sep 29, 2008)

Bad news now the truck won't start


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## DatSoon (Feb 11, 2009)

Have you made any headway on your truck? I'm having the exact same issues with mine. I have the procedures to adjust your tps, which is also the idle switch combined in one. The idle switch is your culprit. Disconnect your harness from the switch and put a jumper wire between the two bottom connectors on the harness side. Set your idle at ~1,100 rpm. Then using a voltmeter connected to the bottom two prongs on the idle switch, move the the switch until you find the on-off point (showing 5 volts on and off). Tighten up the screws and plug in your harness and you are done. I can send you a scan of the 1986 nissan electro injection supplement manual if need be.


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## dongatta (Sep 29, 2008)

I have made a little progress. I did find a rather nice vacuum leak on my bp valve hose. As far as the tps I can't seem to get it adjusted correctly. What exactly were the symptoms your truck was giving. That would be great if you could send me the supplement manual. also thanks for your reply


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## jblakeslee (Nov 30, 2005)

DatSoon said:


> Have you made any headway on your truck? I'm having the exact same issues with mine. I have the procedures to adjust your tps, which is also the idle switch combined in one. The idle switch is your culprit. Disconnect your harness from the switch and put a jumper wire between the two bottom connectors on the harness side. Set your idle at ~1,100 rpm. Then using a voltmeter connected to the bottom two prongs on the idle switch, move the the switch until you find the on-off point (showing 5 volts on and off). Tighten up the screws and plug in your harness and you are done. I can send you a scan of the 1986 nissan electro injection supplement manual if need be.


 Ok....according to this you check the bottom two prongs on the idle switch, moving the switch until you find the on-off point......then tighten up the screws and plug in your harness......my question is: how do you have five volts at the switch with the harness removed? Do you tighten the switch down at the point where the volt meter moves to 5v or at zero just before it moves to 5v?


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## DatSoon (Feb 11, 2009)

Check this out. Picasa Web Albums - Curtis - 1986 Electro ...
The book doesn't mention it, but If i remember right I had to jumper the wires between the harness and the idle switch. I set the switch to the point where it was at 0, then moved to 5v as throttle is opend. The top prong is not used on this truck. It was used in other applications with an automatic transmission. It sent a signal at wide open throttle.


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## jblakeslee (Nov 30, 2005)

DatSoon said:


> Check this out. Picasa Web Albums - Curtis - 1986 Electro ...
> The book doesn't mention it, but If i remember right I had to jumper the wires between the harness and the idle switch. I set the switch to the point where it was at 0, then moved to 5v as throttle is opend. The top prong is not used on this truck. It was used in other applications with an automatic transmission. It sent a signal at wide open throttle.


Thanks...I figured I would have to rig some kind of jumper because there is no way you have power at the switch with the harness disconnected....just checking to see if you found some other way to do it.....


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## dongatta (Sep 29, 2008)

Thanks for the replies and sorry for the laps in time. I checked everything as instructed and I only got voltage on the tps plug side no voltage from the tps. Also i tried two different tps's and the truck drives with the tps unplugged am I missing something


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## CMax03 (Jan 17, 2009)

Vacuum leak?


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## dongatta (Sep 29, 2008)

Where possibly would the leak be I assumed that if the tps wasn't even plugged in the truck would not run


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## CMax03 (Jan 17, 2009)

brake booster air leak!


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## dongatta (Sep 29, 2008)

The brake booster and master cylinder were both replaced from comments from previous posts I am just at a loss


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## CMax03 (Jan 17, 2009)

sounds like a defective exhaust coil to me!


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## dongatta (Sep 29, 2008)

How would you troubleshoot the coil to determine that it is the problem?


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## zanegrey (Dec 5, 2005)

i do not think this is a coil ... however ..

check coil and ballast for cracks .
check the plugs and wires for corroision and cracks..

this engine has one coil so if it was not working the truck would not start. imo...

kinda sound like you might have crap in the gas tank..


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## CMax03 (Jan 17, 2009)

put a timing light on the exhaust coil @ idle watch for any misses in the light image. Racing engine and exhaust should switch off, accelerate engine slowly the coil should fire then release throttle and the coil shut cutoff during decel. If it's missing during idle it's missing at part throttle acceeration!


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