Car running strange...

[PMan_S13]

I've made a post about this in the Tech section. Hoping to find someone who has come across this problem, and solved it.

Rebuilt '91 KA-t, 8.5:1 compression, 370cc injectors, s-afc2, recirc bypass valve, no emmissions junk, nothing else would matter.

After some other annoying problems I've solved, the motor will start and run fine. The problem is it is idling way too high (2k) when it is hot or cold. Checked everywhere for any type of leak, nothing. Since all the emmissions are gone, there is not a lot of places for vacuum to leak out of. I've tested all with a vacuum tool, all held pressure pretty well. Can't really check the timing since it never gets lower than 2k. But at that speed it is at about 25-30 btdc, which is close enough to not matter to idle, I think.

Now it may seem like I just need to turn down the aac, but the other problem is strange. If you rev it up at idle and let it settle. It will decel down to ~1400 and then stop and something changes. It then runs very rough, no stumble or anything, just roughness. This lasts about a second at most then something changes back and it speeds up to 2k again.

I assumed this was the ECU pulling timing. Timing gun shows about 10-15 btdc when it is rough. It then changes back. So I pulled back a lot of timing, as far as it goes without moving a tooth. It starts and idles at ~1450. Revs up and idles back down no problem. Check the timing 5 ATDC. Runs really rich, no power, kind of unstable. But when I switch it back it does this cuttting out again. Once again, it doesn't go rough until it has idled down that far. It doesn't cutout while I am revving it up. So now I guessed that it must be off a whole lot of timing and the ECU is pulling timing on startup. Negative ghostrider, ignition timing is spot on. If you disconnect the TPS it revs to ~2700. On reconnect it does the roughness at 1400 again and then goes smooth to 2000 as always. Don't want to drive it unbroken in wiht it all messed up, but I have driven it a mile or so. Drives just fine. I got it to act even weirder just a little while ago. Revved it slowly to 3500 and let go. It did the roughness as suspected, then revved slowly to 2250 at which point it went rough again. It did this like 5 times, I finally blipped it and it stablized to 2000 like before.

Frankly I am at wits end with this darn car. Here's a list of things I have tried.. Someone PLEASE help...

-Reset ECU, ->nothing significant-Reset S-AFC2 (Motor in not broken in or tuned yet, -27% across the board) ->nothing-Tried pinching Air regulator, too remote, so I disconnected it -No change when warmed up.-Checked timing ->good-AFM is good. Just got newer one.. old one made idling impossible (bad element)-Pinching main idle line will make it idle down, even kill it.-checked TB closed voltage -> 0.5v-Replaced 02 sensor ->Seems to work, runs a little on the rich side, but can be easily set correctly with the AFC (I left it at -27%) which doesn't change much except the smell.-Hicas needs to be bled, or at least the little light is on. Doubt that makes it run differently, but might as well mention it. PS level is good.-oil level is good-engine light works, but doesn't flash.

That's all I can think of at the moment. Again, someone help.. I'm really tired of driving a Neon.

[LongIsland240]

does the tps voltage increase/decrease fluidly (no dead spots)?EGR disconnected/capped?....I would assume yes since you said you have no emissions...Idle air motor/TB clean?(no sticking throttle plate or gummed up iac)....You just changed the MAF- is the element clean? (spray it off w/some electronics cleaner)Tough to diagnose a car without having it in front of you....but keep us posted on your findings with it maybe it will become a little clearer...

[PMan_S13]

On the sensor check of the AFC I can move the throttle from ~0.5 to ~4.060 pretty smoothly, no dead spots.

Yeah EGR is sitting in a box in the basement, made a plate and used sealant to cap it off.

Not sure what a Idle Air Motor is, but the throttle body is good, doesn't stick. I see where you're going with this, but I think it is more electronic than mechanical since it snaps on and off so quick.

The MAF should be good. The reason I switched was because once I got the motor put back together it would start, but ran really bad and would not idle at all. Nistech pointed to the AFM. Got one off a guy who had 2 extra from an s13. It started right up and doesn't seem to be a problem. BTW, if the maf is disconnected it will still make this momentary roughness. So it should not be related.

[PMan_S13]

Maybe it would help if I explain the problem better.

Ok, startup.. goes to about 18-1900, slowly works its way to about 2000 and just sits there. Once it is warmed up it doen't really change engine speed. At least not that I can tell. If you rev it up to any engine speed, it revs fine and smooth, then as it is slowing down, it will idle down (still smooth at this point) until it gets to about 1400 then it stops and stays at ~1400 and does this roughness. The roughness is audible, not pinging or knocking. Just like I said, sounds like "bRRRRRR". It is still firing on all cylinders and is stable. Then about a second (sometimes only momentary, or barely there at all) later it will change back to how it was before and go up to ~2000 again.

That is pretty much the problem in detail. Tomorrow I may try to get the idle down much lower.. I haven't tried yet since this seems like a more trouble, but we'll see how that goes.

[PMan_S13]

Um,... you should not be able to start the engine if you hold it at full throttle right?

I was going to check the TPS but before I did I just sort of remembered you shouldn't be able to start it at full throttle. Decided I might as well check it and it came roaring to life unexpectadly.

[PMan_S13]

Getting a bit closer...

Following Nistech's advice I moved the stopper on the TB back to it's original position. But I noticed the threads were dirty higher up (like they have been exposed longer than the rest. So I moved it up to there. Now it revs and decels without that stupid roughness. Just a word of warning. DO NOT move that stopper, it is adjustable but is not meant to be adjusted. Kind of a strange idea, but whatever.

I'm wondering if someone can look at their s13 TB and tell me how many threads they can count. That way I can get it as close as possible to a working model. Then I just need to calibrate the TPS voltages and it should be sorted out. It's a little rough now, but I'm sure it's cause of the false TP readings.

I tried toying with the idle screw. It doesn't change anything really. The only thing I can see that would make this happen would be either the car wants to idle but the idle valves are locked open. Or the car isn't idling and actually is at partial throttle, so idle adjustments do nothing anyway. If I get the TPS and that little screw on there good then the only thing left is the aac or othe idle valves are gunked up.

Any thoughts?

[LongIsland240]

Getting a bit closer...

Following Nistech's advice I moved the stopper on the TB back to it's original position. Now it revs and decels without that stupid roughness. I'm wondering if someone can look at their s13 TB and tell me how many threads they can count. That way I can get it as close as possible to a working model. Then I just need to calibrate the TPS voltages and it should be sorted out. It's a little rough now, but I'm sure it's cause of the false TP readings.

The stopper only sticks up about 2 threads..maybe 3 (the side that actually sits against the arm) on mine, i've never touched it, so i would assume it's correct.

I tried toying with the idle screw. It doesn't change anything really. The only thing I can see that would make this happen would be either the car wants to idle but the idle valves are locked open. Or the car isn't idling and actually is at partial throttle, so idle adjustments do nothing anyway. If I get the TPS and that little screw on there good then the only thing left is the aac or the idle valves are gunked up.

Any thoughts?

You said tps reads .5 @ idle..this seems ok..maybe even a touch low (i don't know the spec for this car but most i've come across are around .8-1.0)

Keep me posted...hope that helped

[PMan_S13]

2-3 threads, huh? I think that's even lower than where mine is now. My TB might still be open enough to left some intake air squeak by. If anyone else could please check then I can kind of use the average.

I checked the specs in the fsm. Fully closed the TPS should read .4-.5v and at full throttle it should read about 4.0v. That's what I'm going to try and set it to.

I gotta work night shift all weekend so I won't really get a chance to tinker again till Monday morning. A guy has to get his sleep =/

Thanks for the help.

[PMan_S13]

-UPDATE-

Well since my last post the following has been looked into.

-Took off the AAC and the Air Regulator and cleaned them. Nothing irregular here, no clogging or gunking. Parts moved freely. Reinstalled.

-Took off the throttle body. Set the TPS screw just low enough so that I can cup my mouth over the end and blow and it will hold pressure. I wanted to take off the TPS and see if the connections wer corroded or broke, but I realized that thing is pretty well sealed. Reinstalled.

-Checked to see if the gasket between the intake and plenum was blown. Looked fine, but I put some silicone sealant on anyway so it makes a nice fit.

-Checked all the wire connections for the S-AFC2. Nothing looked bad, but I regreased them and taped them up again.

-Realized that the throttle cable was not set right, so that even when floored it would not give full throttle. Fixed this so it can fully open and fully close now.

-After all the above was back on I set the full throttle voltage to about 4.0. This made closed voltage 0.415v, so I set it back a little to 0.5v.

Ok, well once I got everything back together it is acting completely different. First off, it will not start without some throttle input. It does not idle at all, and it generally runs bad. You must keep your foot on the gas to keep the motor going. I had it once or twice just barely running at 200rpms or less without throttle, but this was momentary. I can smell raw gas pretty strongly out the tailpipe, so it's way rich.

I think I might have had a small leak in the plenum gasket but fixed it with the silicone (Which might be why it idled high before but doesn't even try now). But I think that TPS has been an on going problem this whole time... maybe not tripping the idle switch and/or offset from where it needs to be.

Anyone want to chime in?

[:: orion ::]

You cannot set the idle properly via the IACV with the TPS plugged in...

Try disconnecting the TPS and setting the idle via the IACV...

If it wants to die if you let off, turn the IACV screw full conterclockwise (high idle), then try again. If it idles w/o throttle input, then turn the IACV adjustment screw until you get 650-700rpm (per the FSM, IIRC)...

Then plug the TPS back in, and report what happens.

Good luck - Brian

[NISTECH]

The throttle stop screw is different for every throttle body. It is the calibration for that specific throttle body. The maching specs are not tight enough to have them all be the same when they are made so that screw is needed to make them all have the same throttle plate to chamber gap.So you can not set it by comparison with another 240. Before any one asks No I do not know the spec for the gap and am not sure if it is listed in the service manual. I have never had to make that adjustment on any nissan and have always been aware to never touch that adjustment.

[WDRacing]

Far to many use that screw to play with the idle...only to screw up how there car runs.

[PMan_S13]

Got some good news, not great but good. But I feel guilty for making two posts in seperate forums for the same thing...

-here's the thread if you want to read the news.http://www.nissaninfiniticlub....01165