ALD and closed throttle stalling

[GTP091]

I've been looking at getting a datalogging system for a possible turbo application I would like to do in the future. Is there any merit to getting this early for maintenance purposes as well? Im under the impression it gives out the engine sensor readings and the general condition of the engine running info. Right now my engine sometimes stalls after it heats up to operating temp. When idling at a light and the engine is warm if I accelerate and then ease off the throttle the RPM dips so low the engine sometimes stalls. Almost like the IAT is to slow to respond ( the IAT is almost new ) to the closed throttle. Does this very often when pulling into a parking lot when coasting, or taking a slow turn through a light only after I let off the gas. It only does this when warmed up so I think maybe the O2 sensor is bad ( closed/open loop??). Also the engine has a random miss when idling as well ( I have Bosch +4 - might be the culprit ) and I would love to see the results of a read out. any ideas on the o2 sensor and/or datalogging?? Engine is great other wise but it could leave me stalled in the middle of oncoming traffic someday!

I have replaced - TPS, CPS, ECM, plug wires, knock sensor, redid timing, ICM( have 3 units same result), EEprom, the list goes on. all but O2 sensor and coolant sensor...

[jmgtp]

I think you meant IAC (idle air control) rather than IAT (intake air temp)?

I'd start off easy by clearing out the IAC passages with some carb cleaner and maybe running a can of gm top end cleaner through a vac hose. Reset the IAC (theres a key on/off sequence I believe) or if you get the datalogging software you can usually reset the IAC through the aldl port. Other than that you may have a small vacuum leak. Check for unplugged vac hoses and you can also try replacing the upper/lower intake gaskets. There were also claims of stalling due to an issue with the fuel injectors on the earlier years though I don't know if they were true or not. I've been running injectors from a 97 dohc without a problem, they also don't tick loud like the 91 injectors did.

When I first got my car it, many years ago, it would do the same as what you describe. Occasional stop light stall, turning into a parking lot stall, etc. My issue was resolved by replacing the upper/lower intake gaskets which are still very cheap for the 91-95 motors.

If you have a laptop I'd say definetly invest in an aldl cable if you plan on servicing your car yourself. You'll be able to monitor all the sensors and engine operation in real time as well as create a recording to dump into excel. The cables are pretty cheap (certainly under $100) and you can find some good software for free like TunerPro and Freescan. I use an aldl to serial cable with a usb adapter and TunerPro.

edit: on a second read through of your post I see you're using the bosch plugs. I've heard nothing but bad. I'd start there.

[GTP091]

ya IAC not IAT my bad.

I did the port and polish on the intake and cleaned the hell out of the intake so Im sure there are no passages blocked. The problem existed before I had the timing done ( paid a shop ) and still did afterwards so between the P & P and the timimg there have been two sets of upper and lower gaskets on it so I don't think it's an intake leak. I also nosed around with various 'stethoscopes' to hunt for vacuum line leaks and found none. the IAC reset is the same as idle relearn is it not?? never heard of IAC reset.

I thought about using seafoam to clean it out napa has the stuff for about $12 but it seems pretty sketchy and no one has a real firm answer as to what vacuum line to dump it into. Sounds like this stuff is potent and could eat older rubber vacuum hoses and silcone gaskets??

I do wonder about those plug,s I started thread on it awhile back and ended up with a heated debate and not a massive amount of answers. Some guys have them and say they are just perfect. but maybe it is time to pull the buggers out, would be to bad, they sure do look purty and technoligically advanced... Screw it might as well delco 42LTSM right??

Is it a bitch to get the datalogging systems to work with USB or pretty easy?? Im very interested in the 02 sensor as it's the only thing I haven't ruled out.

[jmgtp]

I can't get Freescan to work with the USB adapter but TunerPro works like a champ and seems more functional to boot!

The idle relearn is, I believe, a key on/off sequence that moves the IAC back to the factory preset. What I am referring to as an IAC reset is something you can do through datalogging software that does the same thing, however you do it with the click of your mouse - plus you can do it while the engine is running (usually stalls it out but at least then you know it worked).

Start with plugs though. I'm not sure the # but the parts store should be able to look it up easily enough. I did a timing belt on a dohc a few years ago, the owner gave me bosch plugs to put in. I didn't want to but they insisted. I don't think it went 3 months before it was misfiring - they replaced the plugs with regular delcos and it solved the problem.

[mrl390]

The seafoam goes in your brake booster line. 1/3 bottle in the line, 1/3 in the oil and 1/3 in the gas tank. Turn your car on and remove the brake booster line from the booster. Let the vacuum suck up the seafoam a little at a time, making sure not to stall the engine. It will spit and sputter but dont let it stall. After it is all sucked up, turn the car off and put the booster line back on the booster. Let the car sit for 5-10 minutes. Put the seafoam in the gas and the oil while it sits. After the 10 minutes, go start the car and enjoy the show. Rev it up a little if you like. Run it until all the white smoke is gone. Maybe drive it around the block a little. You will need to change your oil after about 100 miles of putting the seafoam in. I did it in my old 93 F150 and had no problems with it eating the rubber lines or the gaskets. Alot of people use the stuff.

[savannaz34]

me too

i also have have the same frickin problem with my 91 z34.
only when the engine is warmed up,it will stall when you let off the throttle to turn.and some times when you come to a stop at a light.parking lots are also a real pain in the ass

i just plated mine 2 weeks ago to drive for the summer and then the wether got frickin cold two days later,on the first cold day i went to go to work.and i think i found my problem.
there is a vacum leak in my left fender where that vacum ball thingy is.
cant hear it when it is warm out side.one day(who knows when)i will investigate further.wouldn't hurt to check yours

[walterdude]

IAC RESET

Here's a copy and paste of a post I made a short time ago about replacing/resetting the IAC....
Also included a link to "how to relearn the idle" (NOT the same as IAC reset...)
Hope it helps,,,
Tom...

-Before installing a new IAC valve assy, the position of the pintle must be checked.
-Measure the distance from the gasket mounting surface of the IAC assy to the tip of the pintle.
-If the distance is greater than 1 1/8" reduce it by applying firm hand pressure on the pintle to retract it.

"""Note: the IAC resetting is controlled by the ECM. To initiate this process turn the ignition on for 5 seconds,,, turn it off for 10 seconds,,, then start the engine and check for proper idle..."""

OBD1 Idle Re-Learn Procedure:

http://60degreev6.com/content/Idle_Relearn

[GTP091]

i also have have the same frickin problem with my 91 z34.
only when the engine is warmed up,it will stall when you let off the throttle to turn.and some times when you come to a stop at a light.parking lots are also a real pain in the ass

i just plated mine 2 weeks ago to drive for the summer and then the wether got frickin cold two days later,on the first cold day i went to go to work.and i think i found my problem.
there is a vacum leak in my left fender where that vacum ball thingy is.
cant hear it when it is warm out side.one day(who knows when)i will investigate further.wouldn't hurt to check yours

When I was having the car painted I left the vacuum ball off and blocked with a golf tee. Awhile later I put the ball in as a test but didn't tighten the speed nuts down and it fell out and smashed to hell. I left it open and the car ran the same so I doubt it's my problem. I have since replaced it and and painted the new one even no leaks as I used silicone around the nipple. Did make cruise work 100% no more slowly losing speed...