1990 hardbody high idle and stumbling

[cookj]

Hello. My son has a 2.4 manual with unknown miles. The truck began to idle high about a week ago, and this morning on his way to work, the truck would stumble when shifting through gears and acceleration, like it was starving for fuel maybe. He says it smooths out while just cruising. I'm thinking the high idle may be related to vacuum but uncertain on the stumbling. Will attempt to look at this evening but was hoping to get other's opinions on this. Any information will help. Thanks!

[Cbohannan101]

I am actually having the same issue! I pretty much assume it has to do with the cold start functionality and it may be staying on... Or perhaps the Aux Air valve wont lock to make it not self adjust from engine vibration. My third guess, with out so much as really looking under hood, is that a mixture of things is happening. Build up in the throttle body, possible build up related to the EGR or PCV, crank angle sensor has shifted and is making a misfire detected to the ecu, or maybe the exhaust vapor system has a failing component (Charcoal Canister).?

I'm about to check mine out. I'll get back with you ASAP

[cookj]

alright, thanks! I told my son to stop at a partshouse and have them read any codes, as the check engine light hasn't come on. Also, told him to get some vaccuum hose and carb cleaner so we can start trouble shooting this evening. Your suggestions on checking the crank sensor, canister, MAF,etc is a good one and was where i was thinking of starting this evening. I know about 3 weeks ago he used an entire can of carb cleaner through the throttle body. I also degreased his engine about that time, but, made sure to cover and/or clean all harness connections with contact cleaner afterwards; I also replaced the pcv valve and cleaned the air housing, vent tube and replaced the air filter. I'll post/share what we come up with this evening or tomorrow. thanks!

[raqball]

I had a similar issue a few months back and discovered the problem after I failed a smog inspection.

I replaced the upper and lower TBI gaskets and the EGR gasket. Passed smog and appears to have solved my issue..

[cookj]

Originally Posted by raqball

I had a similar issue a few months back and discovered the problem after I failed a smog inspection.

I replaced the upper and lower TBI gaskets and the EGR gasket. Passed smog and appears to have solved my issue..

I appreciate that and will check into!

[wrenchez81]

FYI.. most parts stores won't be able to read obd1 vehicles.. all he has to do is look under the passenger seat at the ECU and it'll tell you the codes.

[alabama_lowlife]

I had a similar issue that wrenchez helped me locate. It was the intake manifold gasket causing a vacuum leak. It would idle high, then low and sometimes go dead. While I was replacing that I found another leak caused by a vacuum line at the EGR valve.

[Cbohannan101]

1) I am in a repair shop that my family owns... OBD1 will not show you anything valid for information.
2) Vacuum can cause a fumble, or perhaps even a high idle, but the odds of vacuum alone causing a vehicle set to idle at 750+/-50 from the factory to idle at 2000 to 2400 is a bit unheard of in my experiences so far.
3) I also have cleaned out and reuilt my throttle body in the last couple months. I see it need honing in the mani, but all of my lines are physically hooked up. I even have replaced my injector O rings and my fuel hoses at the same time as the cleaning.
4) I can manually lower the idle speed to a more norm level (900 is ok for me), but it creeps higher and higher with drive time. I think direct pressure of the gas petal actually has an effect on how quickly the idle goes up again.
**BEFORE YOU CHECK ALL OF THESE IDEAS OUT, CHECK YOUR TIMING**
Nissan oe standard is to see if too much timing is in the motor and causing detenation or other internal damages.


I wanted to take a sec to spread some information here...

There are 3 screws on a KA24E for sdjusting the idle speed.

The first is on the radiator facing side of the throttle body. The screw is gold and standard headed (completely parallel with the ground and in a recessed open ended cast tube(oe came with black rubber cap, that most likely already has fallen off). **turning to the left will increase speed and to the right will decrease.**

The second is the mixture screw. It is is a spring loaded screw on the back side of the throttle body. DO NOT TOUCH.

The last is the bigger of the 2 rear mounted spring loaded screws, and it allows you to control idle speed "when the vehicle is not up to temperature". Such is not always true. I recommend inspecting to make sure that the 8mm nut on this screw is there and the screw is held down tight, to prevent self adjustment.

[cookj]

(Wrenchez/ Alabama/ Cbohannan) I appreciate all the responses and will look into each. Unfortunately, my son didn't make it by till late, and, i was tied up removing a wetclutch in this ATV. However, i did manage to pull the air flow meter (MAF) and inspect. The wires appeared clean, but, sprayed them down with carb cleaner and re-installed. As it was dark, didn't have time to do much of anything else. As best i could, checked the vacuum lines and did not see any obvious issues; also, air filter and housing was clean and all plug wires were intact.

I started the truck, and low and behold, it idled normal! So, decided to take it down the road. Immediately after backing out of the driveway, i went into first gear and it started to buck/stumble with the slightest acceleration. It cleared up and I was able to make into third gear with no issues. Pulling away from a stop sign, no problems in first; however, after hitting second gear the stumbling began again before clearing up in third and fourth. Long story short, I drove it around the neighborhood with it stumbling intermittently. It basically acts up during acceleration, but not always.

Wrenchez, this may be a stupid question, but how might the autoparts guy check the ECU for codes? Does the seat need to be removed, and/or, is there a port on the ECU for his reader? My son hasn't had this truck long and I'm not familiar at all with these Nissans. Again, I really appreciate you guys helping me trouble shoot this problem. James

[Zerksy]

Had the same problem. turned out to be the throttle body base gasket leaking. thank god for carb cleaner. lol