High Idle/Other issues

ONLY for ADVANCED technical discussion about the 240sx!
Posts: 9
Joined: Mon Dec 07, 2020 3:36 pm
Car: 1990 Nissan 240SX

High Idle/Other issues

Postby Cloren10 » Mon Sep 06, 2021 10:33 am

Finally got the temperature sensor fixed, but still problems about with this bad boy. Completely rebuilt D21 engine with an S13 crank in a '90 S13.

Issue #1 - High Idle

Not sure what is causing this one at this point. I've replaced about half of all of the vacuum tubing on the engine, new O2 and MAF sensors, and sealed up any intake issues I could find. Cleared IACV and EGR out as best as I could. Even if I turn the IACV all the way closed, the lowest idle I'll get at operating temp is 1000. If I put it back to essentially where it was before I took it down it idles closer to 1750 at operating temp. But when I turn it down to 1100 it leads to the next issue which is...

Issue #2 - Heavy shaking

This one has me perplexed. The engine shakes just a bit if you look at it if it's anything over about 1300-1350 rpm. When it goes below that, it shakes like crazy, worse the lower it goes. Turning the IACV all the way shut, I've gotten it down to 1000 rpm and the engine shook side to side so badly, it felt like someone large was constantly shoving it. Tailpipe shaking badly too. If you just looked at it youd see the car shaking side to side.

My first thought was bad timing or a misfire. Ran it with new gas and seafoam (old gas was 6 y.o.). New plugs and new wires on it, and when I give it even the slightest (and I mean slightest) bit of gas it basically goes completely away. Once I left off the gas it's right back to it. I'm not sure if it's a motor mount issue, but I thought that was more apparent when you hit the gas, which is the opposite for me.

I'm quite sure I set the timing right on this thing. Granted, I put the chain on with the little silver dot being two teeth off, but that shouldnt really matter right? All links of the chain appear to be the same, and I put it on at crank/cam at TDC.

Fuel injectors appeared fine, and they should be clean after I wiped and seafoamed them.

Is it maybe a crankshaft balancing issue because I used the S13 crank on a D21 block? The original D21 crank that i got with the engine had some bad journals but my original S13 with a bad block had a nearly pristine crank, so I opted to use that. Had to leave the dust plate off (wouldnt fit) but otherwise the S13 flywheel I reused bolted on fine.

It develops power fine when it's on the road. My buddy drove it up to 4th gear around the neighborhood and given that it only develops like 140hp, it pulled pretty well.

Issue #3 - Engine sound

It sounds like....a diesel truck. That's the only way I can describe it. When I hit the gas it actually sounds pretty good and strong, just like it should, but when it's at idle I get the diesel sound.

It isnt the sound of an engine that's low on oil with the characteristic ticking either, and the machine shop said the valves look fine after I took it down so no contact there. I can get a video of the sound if it helps at all.

Issue #4 - Issues still abound

This is just a miscellaneous problem listing that may or may not be affecting the others listed, if this helps at all. Both tension rod bushings are bad, it leaks a bit of coolant, and for some reason I cant explain, when I start the car, the dash electronics will only start if I give it one good rev, and it will also trigger the windshield wiper for exactly one cycle too when it boots up. Turning the heater on also causes the tachometer to flutter back and forth a bit which is weird, despite no noise change on the engine.

Any advice or troubleshooting conjecture is welcome at this point.

I appreciate you all!


Return to “240SX Technical Forum”