('93 240) Idle Adjustment Via TB? Say What?

[Shift__BODOM]

A year or two ago, I was having low idle/stalling issues, so naturally I took the car to a mechanic (I was a bit naive back then). The mechanic told me he adjusted the idle on the throttle body and now the car idles fine. Not knowing much about my car (or cars in general) at the time, I figured the problem was solved, paid the man, and went home.

A few months later, I was learning a lot about the 240, and decided to check the vacuum lines for leaks. Lo and behold, I had a vacuum leak. Since fixing the leak, the idle has been high. Cold idle was at 1400-1500 RPM, warm was 1100-1200. Since adjusting the idle via the IACV and bottoming out the adjustment screw, the cold and warm idle have dropped a bit, but are still too high. Cold is 1200-1300, warm is 900-1000. Recently I remembered the mechanic telling me he adjusted the idle at the TB, so I went back to the shop to get more info on that, but it turns out the mechanic was fired not too long after he worked on my car, and nobody knew much about my car and couldn't figure out how he would have done it.

Here's where you guys come in. Is it possible to adjust the idle via the TB, and if so, how can I reverse it.

Edit:

After running out and looking at the throttle body, the cable has considerable slack in it - about 1/4 inch play until it engages.

Edit 2:

I'm also going to pull the IACV and make sure it isn't acting up on me, will report back after I'm done.

Modified by Shift__BODOM at 10:24 AM 3/29/2008
Modified by Shift__BODOM at 10:28 AM 3/29/2008

[Shift__BODOM]

Ok, I looked closer at my TB and noticed there was a kind of "stopper" that kept the throttle from closing fully. It was a small threaded bolt (no head) with an 8mm nut attached about halfway down. I loosened that down until the idle was to spec. Of course, the IACV is still bottomed out, but since it's raining now I can't pull it until probably tomorrow. Will update then.

[guyaverage]

You do know you have to have the throttle position sensor unplugged when adjusting the idle, right?

Put the stop screw in spec per the manual then adjust the idle speed (TPS unplugged) via the IACV.

[Shift__BODOM]

Yes, I know you need the TPS unplugged during the idle adjustment via the IACV. With the adjustment screw all the way in, it still idled high @ 900-1000 RPM.

I'm thinking that lowering the stop screw will get me to and fro for today without too many problems, but I realize it's only temporary until I can pull out the IACV and inspect/clean/repair/replace. Then I'll have to adjust the idle the proper way, instead of ghetto rigging it.

Also, a side note, the ECM threw a code 21 - Ignition signal circuit: Ignition signal in the primary circuit is not detected by the ECM during engine cranking or running. Don't know if that's another possible cause for the high idle (doubt it) but I'll run through the diagnostic procedure after I finish up with the IACV. One thing at a time..

[boriquaS13]

My friend if the mechanic adusted the TB stop screw to bump your Idle and you had a vaccuum leak that you repaired you have to undo the band aid the dumb*** put on your car. I think you need to check your TPS voltage if he adjusted the stop screw that should change your TPS voltage. I would suggest you check your TPS voltage KOEO (key on engine off) see were it is set at if its at .6 volts I would adjust the stop screw untill it is at .42 volts. Now this is if Mr. Dumb*** did not also adjust the TPS because it has its own seperate adjustment. Good luck and I hope this helps.

[Shift__BODOM]

Aah, yes, will definitely check the TPS and adjust as necessary. Going to pull and clean the IACV and do a detailed inspection all around the engine bay with my multimeter tomorrow. Hopefully I can get to the bottom of all this.

Thanks for you guys help so far..

[Shift__BODOM]

Well, I finished cleaning up the IACV, but the B12 ate through the gasket and no store I've called has it/knows what it is. Would it be possible to use silicone gasket? I have a tube of Permatex ULTRA BLACK Hi-Temp RTV silicone gasket maker, but on the back of the bottle it says not recommended for use on parts that come in contact with gasoline, and when I pulled the IACV it reeked of unburnt fuel...so...a little help?

Also, more on that Code 21. I went through the whole diagnostic process outlined in the FSM (pages EF&EC 104 and 105) and all procedures checked out O.K. If anyone happens to have any more info on that, please inform me, because I'm stumped. I'll also run a search, since I forgot to do it earlier.

Edit:

I also adjusted the TPS back to spec via the stop screw using an ohmmeter and it idled at about 2000RPM..with the IACV screw bottomed out, before I pulled it and cleaned it, of course. Going to post results tomorrow when I get it in.

Edit:

Ok, I went to a local auto parts store and the guy behind the counter knew what he was talking about (we talked about his Z32 build) and he sold me a sheet of cut-it-yourself gasket. Going to put that on tomorrow (raining again) and report back with the results.

Modified by Shift__BODOM at 4:38 PM 3/30/2008

Modified by Shift__BODOM at 4:40 PM 3/30/2008
Modified by Shift__BODOM at 4:41 PM 3/30/2008

[Shift__BODOM]

Well, after cleaning, there is no change in the idle. I chipped away the epoxy covering the brass screw to make sure nothing inside wasn't stuck or anything, and the spring in there was REALLY loose. Also, the rubber seal that the spring presses against is a bit worn. Not too terribly worn, but a little eaten away.

Like I mentioned in the post above, it also smelled heavily of fuel. I don't know if that's supposed to happen, unless somehow there's fuel getting into my vacuum system, or fuel is coming back into my intake manifold.

I also don't think it was the stop screw that was causing the high idle issue (mentioned in above post 3rd paragraph) because at WOT the ohmmeter read around 9.9 kilohms. Something else is causing the idle issue, and I have a feeling I've got a vacuum leak hiding somewhere. I guess I'm gonna have to hunt it out like the dog it is. Bad dog!

If anyone has any advice or insight into this matter, please let me know, because I'm thoroughly stumped.
Modified by Shift__BODOM at 6:04 AM 4/1/2008

[Shift__BODOM]

Ok, weird thing happened today. I was looking around at all the vacuum lines (which all seem to be intact), and saw that the IACV hose was a bit kinked. I have an ebay-type intake I got 4-5 years ago, and the bungs for the IACV, crankcase vent, and charcoal cannister aren't exactly lined up right.

Anyway, the IACV hose was too long, so I had to cut it, and it's still a tad kinked, but I pulled it off the intake tube while it was running just to see what would happen. The idle sputtered down to about 400RPM, dipping as low as 200. There was super strong vacuum coming out of the hose, and when I plugged it with my thumb for a second and the idle went back up. As soon as I hooked it back up the idle bumped back up to 1100RPM.

What's really confusing me is the way this acted. If I unplugged the vacuum line, shouldn't the IACV pull unmetered air, thus causing the idle to raise? The way this is behaving is REALLY confusing the heck out of me. Would a vacuum leak somewhere along the hardline that runs along the top of the lower intake cause this? I'd really like NISTECH to throw his 2 cents in, since we tried to work this same problem out back in '05 (see thread here for the rundown), and I'd like to pick up where it was left off.

Doesn't mean I don't want to hear anyone else's opinion. I can use all the help I can get

Also, I made a few extra grounds (DIY ground kit writeup here ) and replaced the ripped up stock ground going from the passenger side of the head to the firewall. The resistance from the neg batt terminal to various unpainted screws went down from 10.X ohms to 1.x-2 ohms. woop woop

[Shift__BODOM]

Ok, I've checked every related sensor, every vacuum line (some I couldn't reach, like the ones under the intake runners), cleaned the IACV, even made new grounds (mostly for the heck of it, had bad grounds anyway). Nothing has fixed or even changed the idle. I walked out to the car this morning with little to no hope, when on a whim I checked the fuseboxes.

Turns out the 25A fusible link for "ENG CONT" - my guess is that stands for ENGINE CONTROL (!!!) - was melted down. I don't know how these fuses react when "blown", but this thing was in terrible shape. Would this fuse being blown cause a high idle? I sure hope so, because I'm going to be replacing it later tonight when I have time to get one (busy day today), and if the idle doesn't change, I swear I'm going to shoot blood out of my eyes.

Also, quick question, would the timing being off [at the distributer] cause a high idle? Jeez, this problem is making me want to pull my hair out.

[Shift__BODOM]

Replaced the fusible link, no dice.

So, I'm removing the intake manifold! I figure there's gotta be a vacuum hose cracked or busted somewhere in there, and I need to check the rest of the idle controlling do-hickeys, so I'm going to take the thing out, clean it, paint it and replace every vacuum hose I can get my hands on. It'll also give me a chance to clean all the grime off the intake side of the block and head now that I can finally get my hands in there.

I don't really have to drive this car, and I can take all the time I need on it and pay attention to all the little details. Is there anything else worth replacing in the semi-circle intake trap of death while I have it out? Any tips on actually getting it out? I tried to get the collector out only to realize the starter and oil filter bung are insistent that I SHALL NOT PASS! I guess I'll have to slide the runners out a bit and get another person to hold them up while I slip off the collector. Meh, it'll come. Patience, young jedi...

I realize this thread has kinda turned into a one-man-show, so I'd like to know what some of you guys think about my situation. Even if you don't have any advice or help to offer, post. It's good to hear what others have to say sometimes, and every bit of encouragement helps...God knows I need some right now, too.

[boriquaS13]

Do you hear any hissing at all when the engine is running? How about the intake tube going form the mass air meter to the throttle body any cracks that could be letting unmetered air? Is the throttle plate physically closed in other words look at it can you see any gaps between the throttle body and throttle plate? Check the ignition timing is it correct? Try tapping on the IACV (with the handle screw driver) with the engine running and see if there is any change at all? Man I hope this helps you good luck

[Shift__BODOM]

Do you hear any hissing at all when the engine is running? How about the intake tube going form the mass air meter to the throttle body any cracks that could be letting unmetered air? Is the throttle plate physically closed in other words look at it can you see any gaps between the throttle body and throttle plate? Check the ignition timing is it correct? Try tapping on the IACV (with the handle screw driver) with the engine running and see if there is any change at all? Man I hope this helps you good luck

No hissing, but the engine noise plus the loud exhaust note makes it difficult to hear anything.

The intake tube is aftermarket, thus metal, and I actually inspected it a bit when I was removing all the intake manifold stuff and it's intact.

I'm not sure about the throttle plate, but upon looking at it, it's in the proper closed position and the TPS is within spec, at 1.97ohm(or is it volts...not sure tbh) closed throttle.

The ign timing, I actually haven't been able to check since I don't have a timing light, but would this cause a high idle? See, when it's idling, sure the idle is high, but it purrrrrrrs. There's no roughness in the idle aside from what would be expected from such a large displacement 4 cylinder. I'll definitely have it adjusted after I get the intake mani cleaned up and reinstalled. What I'm thinking is that one of those idle controllers in there are stuck open and naturally I can't reach them without either lifting the engine out or pulling the intake mani.

Tried tapping the IACV, even got a hammer and used it's weight to lightly but firmly tap it in case something was stuck to no avail.

I will definitely get the timing looked at if removing/cleaning/replacing all the emissions stuff from the intake manifold doesn't fix the idle. The distributer is turned all the way to the left, which is a bit suspicious...will definitely get it looked at.

[Shift__BODOM]

Ok, I got the manifold off and right off the bat I spotted a broken vacuum line - more on that in a second. On top of that, all 4 PCV hoses that connect to the intake right before the head were stone solid and all broke off as I tried to remove them.

The SCV actuator/regulator/whatever had a broken bung for the vacuum (I believe), so I'm debating just pulling the whole SCV system out, butterflies and all - they seem to be stuck as it is anyhow, I can't move them an inch. As for right now, I don't want to even THINK about looking into that engine bay for at least a day while I concentrate on cleaning and painting the manifold...then it's on to swapping out every vacuum line that has so much as a hairline crack in it. Plus, I gotta let my sunburn fade a bit

[boriquaS13]

Vaccuum leaks can definatly cause a high idle sometimes there a hard to find. I had a intermitant high idle on my 89 240 it ended up being the intake tube rubber hose off of the throttle body. But then again its an oe hose and it was old. Man I really hope you find/fix your problem. Keep me posted. OH and post a picture of your intake when your done.

[Shift__BODOM]

OH and post a picture of your intake when your done.

Haha, will do. Those things were DRRRTY.

[Shift__BODOM]

Finally got the runners painted, gonna do the plenum tomorrow. I used some spare runners from my S14 motor I had swapped in after I blew my original motor. Anyway, that got rid of my SCV issue, now it's just capping off vac lines to finish it off.

Question, will the S14 EGR solenoid valve work on an S13? The vacuum nipple on my S13 valve broke off with the line attached so apparently my EGR has been inactive/constantly active, depending on how the solenoid works. I don't really want to deal with the crapshoot that is the local pick-a-part or their outrageous prices. I've ruled out the SCV solenoid since it's "on" signal I believe closes vacuum, whereas the EGR solenoid closes vacuum during an "off" signal. Could be the other way around, but ya get my point. Would be awesome if they were the same unit, though, since I'm not gonna be using the SCV anyway.

Also painted the valve cover, which turned out meh, so I might redo it. Pics as soon as I can upload them. My data cable broke and I'm too cheap to get a digital camera so I'm using my phone's camera. As soon as I get off my duff I'll get a cable.

[Shift__BODOM]

Well, no yard around here even has that vacuum 'web', or the solenoid, so I'm just gonna pull all the emissions and block off necessary stuff. Going to go turbo soon anyway (if all comes together properly), so I might as well get this out of the way while I have the intake mani out anyway.

Got the whole intake painted and it's all curing in the garage as I type. Gonna be a few days until the EGR block off plate gets here, so I think I'm gonna take some time off this whole deal and get some R&R. So glad I don't have to put all those damn vacuum lines back in, it's gonna simplify the reinstall SO much. The only problem is I think one of those lines in that rat's nest went to the FPR. I sure hope not, but I'm sure I'll figure it out.

Pics as soon as I can get them up, promise.

[Shift__BODOM]

Ok, I've figured out that the FPR can do with just any vacuum, so I'm gonna use the little thin nipple on the plenum to feed it.

Gonna take off the masking from the plenum tomorrow and let it cure further. While I had all of the wiring loose around the front, I figured I'd clean up the upper timing chain cover. It was pretty much covered in the thick gritty road grime mixed with oil (leaky valve cover gasket) and PS fluid. I would've cleaned off the lower timing chain cover but my back was aching so bad and my knees felt like they were going to break backwards, so I called it a day there.

Just for further dress-up, I painted my intake tube (CAI) the same color as the intake mani (Duplicolor Engine Enamel - cast coat aluminum) and it's coming along rather nicely. I also painted the metal vacuum tubes that feed the IACV and PCV the same color as my valve cover. I'm not revealing the color just yet, but it should look very nice when it's all together. With the addition of all new vacuum lines, the intake side of the engine is gonna be nice and clean. The exhaust side however...not so great. Gotta grab a header, but I'm planning on going turbo soon (like in a few months) so I don't want to feel like I'm wasting money on a header now just to look good. I guess I'll have to do with the ratty rusted exhaust manifold and super clean intake side. Oh well, work in progress. (that's my excuse )

Gonna run down to the auto parts store tomorrow and get some new vacuum lines - PCV and that other idle controller thingy with the red waxy plastic stuff over the nut on the back...don't know what it's called, and the IACV line from the unit to hardline and hardline to intake.

[Shift__BODOM]

Got the vac lines along with a set of couplers to replace my old worn out ones. Waiting on the block off plate (still) and a set of 2 "plug tapers" to plug up the exhaust manifold after removing the PAIR/AIV and EGR. If anyone is wondering, Nissan actually makes a part to put into the exhaust manifold after removing those components. Courtesy Nissan has them for 8 bucks each, which is a bit better than 18 bucks each my local dealer wanted. Part number is 14052-21R00 if anyone wants it.

Still waiting. Wonder if my idle will still be high after all this..? I'd be super pissed if it was, but I found 3 vacuum leaks and 4 more possible leaks (PCV lines from intake) so I figure this'll do it. If not...well, let's not think about that.

[boriquaS13]

Any updates my friend?

[Shift__BODOM]

Aside from random fixes/cleaning, no. I'm still waiting on the EGR blockoff plate.

US Postal Service website says it was scanned in the hub here in my city 2 days ago and it's still not delivered. USPS ftl

[Shift__BODOM]

Ok, well, the blockoff plate came in on friday and I finished putting everything in yesterday. The idle air screw is still bottomed out, but at least it idles rock solid at 750RPM.

Got rid of all the emissions, so I have like, 3 vacuum lines now. Idle air, FPR, and brake booster.

Quick question, for the evap canister, would this setup work or what? What I did was routed the vapor line into the "fresh air" line that went into the bottom of the canister.



I don't want to do any damage, but as far as I know, this "fresh air" hose goes into a plastic hose that runs through the sheet metal and "into" the frame. Sounds weird to me, what do you guys think?

[twowheeletex]

I know this thread trailed off, but I was wondering what progress you made if you did anything else. I know at some point you suggested maybe fuel coming into your vacuum system. the Fuel pressure regulator has the ability to, if it fails, let this happen. if a rip occurs in the little diaphragm in there fuel can be sucked into the manifold. I was thinking about this when I was reading the thread. the real thing I wanted to know was do you think this problem is similar to mine in terms of what you did to correct it. should I do this, cause that's what I'm thinking it's coming down to. here is my thread.

zerothread?id=330712