idle is killin me.. please help

[92rsAWD4me]

ok.. I have been fighting this for too long. My 1992 turbo laser has idle issues. I had the idle set at 750 but was kind of missing so I checked the plugs and fixed the gap and while I was at it I decided to check the TPS which was reading .24 volts according to the checking process so I adjusted it and it idled way high like 3000 rpm.. so I went to adjust the BISS and as soon as I grounded the two spots the idle lowered. I adjusted it and when I disconnected the jumper wire it almost died until I hooked it back up.. Idk what to I'm getting so frustrated and I really need some help on this.

 

[misphit]

First, make sure your ignition timing is correct. Then follow the procedure for adjusting the idle position sensor correctly. Next, adjust your TPS to 0.5v with key on/engine off by backprobing the tps plug. Lastly, set the BISS by grounding out the idle connector on the firewall and the pin on the diagnostic port. When you adjust the BISS, let the car idle for a minute or two after adjusting to see if it keeps up the idle that you've set it to.

If your spark plugs are gapped properly and you've followed the aforementioned procedure in the order that I've layed it out, you should be good. If you're still having problems, report back.

 

[92rsAWD4me]

Well I need to go back over everything but I went through that procedure. When I was adjusting the TPS I had to move it all the way one direction to get it close but couldn't get it all the way to .5v without tightening the throttle cable. Once I did that I hooked everything back up but when I started the car up (with the engine cold) it was idling at 3000 rpm. What I did then was turn it off and loosened the cable. Should I have done that or should I let it warm up idling that high and then adjust the BISS from there? I already gapped all of the plugs and had the idle set at 750ish but I am having problems with high hc's only at idle on the emissions check. That is why I decided to check everything out again and found that the TPS was only reading .23v. After I loosened the cable and it idled much lower I let it warm up to operating temp and began grounding the 2 points needed for the BISS adjustment. As soon as they were grounded the idle speed dropped probably close to 200rpm. I know I need to take it one step at a time so.. should I go back and do whatever I need to to set the TPS to .5v and then just try to adjust the idle from where ever that puts me?

 

[Boosted6]

Try removing your IAC and replace the gaskets,that was a friends prob.

 

[92rsAWD4me]

Pardon my newbie status but IAC? What might this be?

 

[spitefire1]

it is your idle air controll!if this is bad your car will idle like crap, try messing with your cas sensor,the sensor next to your thermostat! good luck

 

[92rsAWD4me]

oh IAC is the ISC... I just replaced it so it should be good. I supposed taking it off and double checking the gasket couldn't hurt. How would that explain the huge difference in idle speed with the connections grounded and ungrounded? Since I couldn't get the TPS to .5v without moving the throttle wire does that mean that the TPS is bad or does that simply mean that the throttle cable was out of adjustment?

 

[92rsAWD4me]

Just to let everybody know I have officially lost all confidence in my problem solving abilities and will be taking the car to a shop to diagnose the issues. Also, depending on what these issues are I will be possibly be having a shop do the remainder or the work on the car that it needs to be able to pass smog. Thank you for all of your help but it appears that I have reached the limit of my knowledge and will hopefully learn from this and continue in my love for the car that I have only driven 4 times since December and even then it was either around the neighborhood or to the smog/mechanic shop.. I have decided that I must really be committed to this idea otherwise I would have sold it by now. Wish me luck and I will continue to read as much as I can on here and keep people updated on any and all progress.. Thanks once again for all of your help.

 

[92rsAWD4me]

Just a little update.

I finally broke down (or was broken down by my wife) and took the car to a mechanic since I couldn't figure it out by myself. They had the car for about 20 minutes and called to tell me that the o2 sensor was bad and was likely my problem with the smog issues I have been having. (really high hc at idle with everything else looking good). Got that replaced, only dropped hc a little and still has rough idle. They checked the timing, evap, and compression and all are good. They are still working on it as we speak (third day of diagnosis). I haven't heard anything other than they are still working on it. I know no news is supposed to be good news but the longer they take to find it the more I am convinced that the issue is going to be an expensive one to fix.

Any way wish me luck since my dsm piggy bank is a little on the empty side right now.

 

[brownfinger]

Um...the ISC and the IAV (it's really the FIAV; fast idle air valve) are two different parts. The ISC screws onto the FIAV. The FIAV is the lower portion of the throttle body, with the coolant lines. You may have a bad TPS or battery. I have to crank my (fairly new) TPS all the way over to one side to get it down under.5V. Also, I saw two different TPS values depending on whether or not the engine was running. It was still cold then, and the battery only made about 10.8 V when the engine was off. This produced a lower TPS value than when the engine was running and the alternator was kicking out 14V.
When setting the BISS screw, the ignition timing, and the TPS adjustment, they will all affect each other. It is important that they are done in the correct order and with the proper terminals grounded for each procedure. I'd set the TPS(with the car running, if possible), then the BISS, then the timing. Then I'd re-check the BISS, if the timing changed any.
Finally, the throttle needs to close completely at idle. Tightening the cable will destroy your throttle-body shaft bearings. At WOT the shaft lever will pry against the stop, forcing the shaft against the bearings, wearing them into an egg-shape. Set the cable with the pedal mashed firmly against the floor. Make sure there is .5mm or more clearence between the lever and the stop.
You should have/develope some faith in your skills. I'd bet you're not much dumber than most of the rest of us human beings.
Tell us what those mechanics try to sell you before you buy it. They aren't much smarter than us either.

 

[xioca]

Mechanics will most likely do nothing for your idle surge. They are quite dumb in the regard that they know then general workings of cars.. but not the specifics for each model. Much better off reading up about it on this site.

 

[92rsAWD4me]

well what happened was they changed some gaskets, the egr gasket was messed up and the tb gasket, also they cleaned everything out, the egr channels or tubes or what ever.. and the tb and the maf. And 120 bucks later it is idling smooth and will pass the smog test in the morning... sucks that it cost 120 for stuff I could have probably done myself givin more time but it feels good that this first major hurdle may soon be behind me.

 

[steve]

$120 for three days of work and a new O2 sensor is a deal.

When you started messing with the throttle cable in an attempt to raise the TPS voltage you were in trouble.

 

[92rsAWD4me]

yeah I haggled the crap out of the guy because they did the work without telling me or giving me an estimate so I whined and cried my way to only paying for a couple of hours of labor and I did the o2 sensor myself. Yeah I realized shortly afterward that moving the cable was a potentially grave error and luckily didn't drive it around like that. But everything seems to be in good shape. Idle is steady at 750, doesn't miss, and according the the last pretest they did at 1pm this afternoon it is more than ready to pass the smog check and can finally begin full enjoyment and also full attention to the huge list of other things that need to be done.

 

[steve]

I'll again point out that the TPS VFAQ is wrong for all years. You can't just set the TPS to some resistance. It needs to be set so that it creates a 0.48v to 0.52v output on a 1G. If you take the measurements of the TPS total resistance and voltage of your +5v sensor power you can figure the required resistance but it will vary from car to car.

Good luck with your smog check and then on to better things.

 

[92rsAWD4me]

Thanks Steve. I believe it read .4 when all was said and done.. I would go mess with it and see but I don't want to do anything to it until I have it smogged then I will still probably leave the motor alone for now.. is running better then it has since I bought it so I am pretty happy at the moment.

On a side note, the car was off and it was kinda cool outside when I checked it. With it warmed up and running it would probably read differently right?

 

[DSM1G90]

Question: How does one read voltage across a TPS anyway? Is it about the same as my example below?

From my experiences with doing TPS with Nissan vehicles was to to stick straight pins in the TPS connector right at the top so the pins would make connection with the pins inside the connector itself.

Then take a digital VOM and read across the ground and the output wire of the TPS. If out of adjustment, you would roll the TPS to get close to the .5vdc with the throttle plate completely closed.

thx-DSM

 

[steve]

Most people now have SAFC's or dataloggers. Both allow you to display the TPS output voltage.
The dealership does it with a special tool that is a break out wiring clip. I used to do what you described until I got a logger or measured at ECU connector since it's easier to probe the pins there.

The hard part was getting the lower bolt loose on the TPS so you could adjust it. At first the choices were remove the throttle body or the fuel rail so you could get at it. Then I just started leaving that one not tightened so I just had to undo the top one and the bottom one was just tight enough to provide some resistance to the TPS moving. I stick the palm pilot in the windshield displaying the TPS output and turn the TPS. Same thing for when I adjust the BISS, I display the ISC steps and stick it in the windshield so I can see it under the hood.

 

[92rsAWD4me]

I know there are a ton of posts about this but where is the best place to get pocket logger and is there anywhere that sells the pda and the plugs/software as a kit or do you have to buy it separately?

 

[1GTalonTSI]

Thanks for the description on the FIAV... been meaning to look that one up.

 

[92rsAWD4me]

IT PASSED FINALLY!!

It turns out that my idle issues and smog issues and fuel cut issues were all related.. go figure. I took it down to the smog shop first thing this morning to get the test. I drove it hard on the freeway for a little bit to make sure everything was hot and ready to go and guess what.. It passed my a mile! It now idles steady at 750 and there is no hesitation no fuel cut and no missing at idle. It feels good to see 5 months of research, stress, hard work, self doubt, and of course money pay off in the way you intended. Here are the old and the new numbers for comparison. It always failed at idle never at 2500rpm.

All of these number are for at idle 750rpm.
The test computer measured the idle at 746rpm.

old test
HC (ppm)
max:120
gp: 270
meas:624()


new test
HC (ppm)
max: 120
gp: 270
meas: 2 hellyeah

 

[xioca]

... sells the pda and the plugs/software as a kit or do you have to buy it separately?

Ebay, or make your own there is a schematic floating around and it is quite easy.

 

[92rsAWD4me]

I found a bunch of pdas on amazon and ebay with the chargers and such for like 30-50 bucks and then pocket logger from the web site is like 125ish I think. so maybe 175ish to know exactly whats going on with muh car.. sounds like a bargain to me.

 

[steve]

Buy or make a cable and run MMCd and it might cost you another $30 over the cost of the PDA worst case.

 

[92rsAWD4me]

Whats a good site to download MMCd from and also where to I buy the cable to hook the PDA to the car.. Is that the hot sync or is it something I need to buy or make in addition to the hot sync cable. My electrical skills are lacking and I don't want to risk messing something up.