bad idle, and backfiring when revving

[ken240sx]

Tryin to put my auto 92 s13 back on the road and am having some issues with the idle. I've been modding it a bit first so i'll tell you guys to help narrow it down... put a short ram air intake, new exaust, cat, headers, plugs, wires, regrounded everything, cleaned up the engine bay a bit, cleaned out my MAF and my IAA, i also took out all EGR related items and put a plate where the egr used to be, plugged up all the vacuum ports, and put a breather on my valve cover and IAA tube. I've put my car in neutral, and had the TPS disconnected to adjust my idle, but even then its goin up and down between 600 and 700. then when i connect everything back and start up my car it is at 1500rpm or more for a few seconds and then drops low enough to dim the lights which is around 300 and then pops up to 700ish and goes up and down between 600-700 again. If i rev the engine I hear it bog a little and i hear the pops from backfire, then the rpms dip low again and settle back between 600-700, sometimes if i rev it the engine completely stalls out. I've ran the car with the MAF disconnected and it idles a little better but if i rev it to the 2500 limit, when it goes back to idle it dips to about 500 then back up to the varying 600-700 idle. The gas in the tank is the same gas from months ago, but before the winter i put treatments in it to prevent the lines from freezing and to prevent it from gunking up...but its still old gas, could this have anything to do with it? Any help is greatly appreciated.

[180fan]

clearly a MAFS issue. The oscillating idle, the 2500 rpm limit are both indicators of a MAFS or MAFS wiring issues. Clean the mafs element and make sure the wires are good, otherwise look for a new MAFS and see if that clears up your issue.

[ken240sx]

the 2500 rpm limit is when i run the car after i disconnect the maf, but even the it diconnected the idle still isnt good

[Arrow]

I've got a '90 w/ the KA24E and a similar problem... except that I do not have a really terrible idle, just a little high ~1k rpm. When I disconnect my MAF the car won't idle past 3.5k but for the most part runs smooth. With the MAF plugged in the car bacfires and will rev all the way up... just bogs and hesitates badly...

I assume that it is a bad MAF (in my case)... I just haven't been able to confirm it yet, hopefully by the end of the week though!

Good luck with your issue and I hope that maybe I was of some moderate help... (being that it sounds similar to my problems and I've been told it's a bad MAF, just haven't replaced it yet... trying to check the connections)

[da40]

kinda of sounds like timming bro

[ken240sx]

yeah i've pretty much narrowed it down to MAFS, Oxygen sensor, Timing issue, and dist. cap/rotor.... now all i have to do is test each one to figure out which it is or whhich couple lol....i'm pretty sure my o2 sensor isnt working up to par, so hopefully that will help a little. and i'm gonna get my hands on a timing light today and hopefully see its way advanced and it solves all my problems without havin to replace MAF or dist. but thanks guys for the input..it helps to know what problems other people have and what it is so i can narrow stuff down.

Heres anotehr thing though, if I disconnect my IACV-AAC harness the cars idle drops like it should, but then when i disconnect the IACV-FCID solenoid, the engine speed doesnt change. Is this normal for the engine speed or behavior to stay the same when disconnecting the solenoid, or is it supposed to effect the engine speed. If its supposed to but it doesnt, then its probably a bad one and related to my problems right?

[Z U L8R]

Before you spend a bunch of money & time, try a known good maf. I'm sure you could borrow a buddy's just for a quick test drive.

After that if nothing's changed check your rotor & cap, also feel for any abnormal play in the distributor shaft.

[Arrow]

Hey guys, I'm curious on how easily the 240's can get their timing off? I mean considering that they use timing chains and all, aside from a shotty mechanic is there a likelihood of the timing getting off? I do know that it's possible to jump a tooth or so... but that seems extreme and not too easy to do. Sorry if this is off-topic a bit

Let us know when you solve your problems though! I should be ordering a new MAF later today (inless they have one in stock which would be great). Hopefully I can post up my results tomorrow.

[Z U L8R]

anything's possible. on the ka24de's the metal guide inbetween the two cams that's right in your face when you take off the valve cover, those tend to brake and rattle, they could dislodge and get caught and mess a lot of stuff but it's pretty rare. timing chain motors as with timing belt motors have a tensioner. If your tensioner's weak it could possibly jump time, whether it be sohc, dohc, belt, or chain. All in all though when you understand how this works with that and this sensor works off that and picks up this signal and sends the ecu this or that signal, when you comprehend how all these parts work together, you'll be able to diagnose your problems that much easier.

[ken240sx]

well i didnt get to diagnose it yesterday..but today is the day. first thing im gonna do is check my mafs wiring and see if theres continuity between maf and ecu, then probably check o2 sensor, check the spark for each cylinder, and i'll probably check tps also. but those are pretty much the main culprits i would think. because my iacv seems to be working, and i cleaned it out and it didnt change the problem.

[Arrow]

well, I bought a new MAF and replaced my old one... got some interesting results too. First I immediately noticed that my idle dropped from around 1k (which is the lowest that I previously could get it) to b/w 600 and 700... which is about right given the fact that I tried to turn down the idle previously. But even with this new MAF the problem was still present... So I checked my plugs again, completely fouled - covered in carbon. I have a feeling that the carbon deposits came from me messing with the car trying to diagnose the problem earlier. I say this b/c I probably ran the car through close to an 1/8 of a tank just by idling for over an hour while I tried different things. And I know that the car was running pig rich as I could smell the unburned gas. So my next course of action is going to be replacing the existing plugs and seeing how she runs - hopefully everything goes well and she gets brought back from the grave...

I did notice a hissing / whistling coming from my intake though - right around my pcv valve it seemed... and also a clicking came from the same area when the car stalled (so the ignition was still in the "on" position)... seems like a possible vaccum leak... hopefully nothing too bad though.

I hope that your diagnosis went well and be sure to post back up when you find your solution! GOOD LUCK!

[180fan]

ah fun stuff those vac leaks. fun like taking a midterm you didn't study for.

[ken240sx]

well just my luck i get called into work, and got out at 9 hoping somebody around me carried a timing light that was open, but no luck. so i had to wait some more. but today i got my new oxygen sensor in the mail and i put 2 gallons of 91 octane in my empty gas tank, empty enough to make a spattering noise on the bottom of the tank when i started pouring the gas in . but anyways, i work 8 hrs today, tommarrow, and monday which sucks, but i'm gonna try to get some time in on my car in the morning tommarrow and mond and narrow this ****er down to maybe one thing hopefully.

[ken240sx]

well all i got to today was replacing 02 sensor, this helped the eradic idle quite a bit. I fixed the timing cause it was a little off. but i'm still having the major problems, these thigns only cleared up some minor issues.

If i'm idling the rpms are steady on 700 without a jiggle in the needle, and timing is pretty much dead on now...but every 30 sec or so the car drops to 500-600rpm and the timing shoots all the way to the other side of the timing notches, then the idle goes back to normal and the car does this repeatedly to no avail. I found out if I just touch the throttle with a feather touch the car just dies.

I cannot run diagnostics because i cant keep the car at 2000rpm or race the engine like the fsm says to. when i try to bring the rpms up to 2000 the engine bogs and barely makes it and i hear plenty of backfires, it sounds like its still running pig rich.

I'm pretty confident now that its not an ignition related problem, not a vacuum problem, not a timing problem, not an 02 issue, and not an emmissions related problem(because i yanked all my emmissions junk after i started having problems because i just dont like them )

The only thigns left i can think of are MAFS, ECT, TPS, and Crank position sensor??

any other ideas would be very helpful, thanks for the input everyone thusfar

[ken240sx]

bump

any idea's?

i'm thinking about going out on a long shot and getting one of those consult cables and the apps for the laptop and i'll tell you guys if its worth it. I mean, if it doesnt work right, i'm gonna return the flippin thing.

[ken240sx]

knock sensor??

anything lol i'm dying

[Arrow]

I'm about to go install my remanufactured MAF and new spark plugs (b/c my old ones got fouled while I tried to troubleshoot it) and see how things go... I hope and pray that everything works well and that my car runs again... I'll post the results when I get back

[ken240sx]

hope things get cleared up, i sucks not being able to drive it

[Arrow]

Well, I made some progress... seems to be that the new MAF did help things... but it seems like that might not have been the only problem b/c I'm still having some issues. The car coated the new spark plugs with carbon in a matter of minutes so that bothers me (I tightened the brake booster vaccum line b/c it wasn't tight)... not completely sure if that was the total issue or not though.

But what is promising is that the car will rev up w/o backfire (nothing big at least and only on the decelleration of the engine). The car seems to rev like it did before... but the only problem is that to get it to rev I have to push the petal a decent bit (maybe close to half) otherwise the car will bog and hesitate... so needless to say there is still something up and I'll have to find out what it is - hopefully soon

Good luck w/ your car!

[ACESXX]

do yo have a power shortage???I did and the car was crappy as hell when I was about to stop in a stop sign and put the car in neutral the car would do some sputtering and stuff like that and when it was just sitting (stalling) it sounded like it was reallllllly rich!!.

[ken240sx]

what kind of power shortage, like what caused it?

[180fan]

Ken did you also check to make sure your injectors aren't sticking open or leaking? The typical stuff that kick the bucket are MAFS or injector related stuff that make your engine go emo. So if you've already done the timing check, and mafs check (which I still think is the case) check the injectors. Bust out the multimeter and see what resistance you get across the actual injector pins and post those up. Other thing you might want to try are the o-rings on em too. Cheap and good maintainence later on down the road.

MAFS I've wrangled with and it can be a real headache to get it to work right when it's acting up. I had idle issues a few years back and that was with 2 good mafs but turned out to be a wiring issue to the ecu. So you may be in for pulling and testing soon if it turns out the culprit is not the mafs itself or the injectors.

[ken240sx]

i checked the injector resistance and they were all the same, i forget the exact resistance but they were within factory specs. I've done a power balance test to see if there is one or more injectors that are bad, but all of them make a drastic change when i unplug them, so i've started to rule out injectors...I was thinking though fuel pump or pressure regulator, the guy who owned the car before me said he replaced the pump, but he also said he replaced the rotors and pads, and when i checked them after hearing squeeking about a week after i bought it they were down to the metal and rotors were spent...so the guy bs me, i didnt bother checking the brakes when i got it considering he said he changed them and when i test drove it i didnt feel or hear anything outa the ordinary. so maybe he bs me on the fuel pump too, who knows. but yea I'm gettin a new mafs soon to see if things get any better, from there im just either gonna take it somewhere and have them hook up a consult or see if that laptop one i've seen in forums around here is worth a penny. I just sorta want to be able to fix it myself because i like the challenge and the work, but since i dont work at a garage or dealer anymore i dont have access to a consult or really too many usefull tools at all.

[ken240sx]

i feel like i should check injectors again tho, so i probably will do more than just power balance and checking resistance. if anything, it wont hurt to get them rebuilt...i'd like to have them running their best anyway so even if they are working ok or not, i still will probably ship them out for rebuild.

[180fan]

Well to give you a heads up on injector rebuilds, DeatschWerks gives 10% off for NICO members. The other thing with the injectors is corrosion on the plugs. I ended up having a greenish/yellow colored corrosion on the male and female plugs. some electronics cleaner and a small screwdriver along with some scraping did the trick on both ends and tightened up the female end by bending in slightly the contacts and that freed me from my rough idle demons on my old SOHC.

Bastards that sell cars to folks and lie about em piss me off like nothing else. Next time you're around the back near the fuel pump terminals, poke around with a multimeter and find out how much voltage you're getting to the fuel pump. If you've also got access to a fuel pressure gauge that'd be another thing to check out for sure.

[ken240sx]

well i found out the hard way that the brakes were down to the metal, about a week after i got hte car it started squeeking and i was like, damn did they not put them in properly or do they need to break in? and then at one point when i stopped at a stop sign and went to go my car felt like it was being held back and i gave a little bit more gas and then heard a big BANG from the back end. I had no idea what happened but i figured it was bad and had to do with the breaks. turns out metal on metal can get catchy sometimes and one of the pads of the rear passenger side got yanked right outa the caliper and destroyed it. the piston was a bent mess and brake fluid was running all over. so i check all the brakes and turns out i needed to replace rotors and pads on all and also the calipers in the back. so an extra 300 some bucks i had to put into it... pisses me off cause having breaks in that condition could have endangered my life. good thing thay failed when i was taking off from a stop in the neighborhood and no in the middle of stopping for an intersection.

but back on the fuel, i will be testing the pump, and also get a pressure reading next free day i have. i'm probably gonna check all wiring goin from maf to ecu and all injector wiring and harness connections.

[180fan]

yikes to the brake failure.

[Arrow]

While you're checking connectors look at your engine / coolant temperature sensor. That seems to be the next logical step in my troubleshooting story as NISTECH is advising... That and I know that the connector is crappy b/c if I touch the wires the car goes to heck and wants to die (this has been going on longer than my recent problem though - I just think that it might verywell have gotten bad enough or combined with a few things to bite me in my butt

Good luck again!

[ken240sx]

yea i keep forgetting about that damn ECT...before some of these problems started occuring i remember that damn thing kept sliding off because i was taking apart a few things so i had maybe another inch of clearance to put back on one of the coolant hoses attatched to the TB and the little metal clip that holds it there disappeared into the engine bay when it flew lol. Since then the ECT has not been staying put...I suspected this was part of my problem in the beginning, but i've replaced the metal clip so it stays on now..but maybe its just damaged now.

[mr2lickit]

IDK if this will help, but I run my car with my o2 sensors disconnected and no transmission harness. My car runs perfect. I had a similar problem and it ended up bieng my spark plugs. If you just checked them and didnt replace them, then I recommend replacing them anyways. They only cost about $2 dollars each. Besides that I would just make sure all the connections are tight and the maf.