Stalling sometimes at stops?

[rufcar]

Recently on occasion my 90 zr1 stalls when rolling to a stop. On even rarer occasions it will throttle. On my old 89 bentley it was the idle control valve. Is that what's doing it on my 90? If so where is it located? Tkx jim f

[-=Jeff=-]

What are you doing in the rolling stop? Meaning are you slowing off brakes and motor? Or clutch in and it is neutral?

Have you put a scanner on it to see what it is doing? Specifically IAC steps and fuel.

Also what PROM is in the car?


I just went through this on my car, someone befor me modified some tables and that caused issues, I but that is one of many things

[WARP TEN]

This happened a bit after Marc did his 510 package on my '95. I stopped by his shop and he made a slight adjustment to (I think) the throttle stop and it was fine after that. My recollection made not be entirely accurate, as it was about 8 or 9 years ago, so I would suggest a call or email to him to see what he recommends. --Bob

[XfireZ51]

Marc probably closed the throttle plates slightly to increase IAC steps.

[rufcar]

One of the previous owners had Marc do.many things and it's been fine the last 20k +/- mi. So this is new .it started after the 1st 1k mi I drove it. The only electronic item I did was clean the grounds and codes for the frame sensors.
Again can it possibly be the throttle control valve if I have one? Tkx jim

[WARP TEN]

Marc probably closed the throttle plates slightly to increase IAC steps.

Entirely possible Dom--I just can't remember exactly what he did. --Bob

[XfireZ51]

Well I guess we can ask Marc next week. Closing the throttle plates causes the ECM to increase IAC steps in order to maintain commanded idle speed. This gives the ECM more ?headroom? to control idle speed.

[WydGlydJim]

One thing to give a quick check to, is these PCV vacuum blocks common to the '90.....depending on the mileage, they can become oil soaked, and then not seal very well.....they are at the driver's side front of the plenum kind of tucked up in opening a bit......push on them a bit, and if they leak a lot, they should be replaced. They can cause erratic idle due to vacuum leak.


https://imagizer.imageshack.com/v2/1024x768q70/923/ngtGRK.jpg

[rufcar]

Spoke to Hibeck today. Thinks it might be a semi stuck throttle. Just document it if and when it happens.

[XfireZ51]

Had that issue w mine a number of years ago. I have a 63mm TB so no dag. Throttle return springs get weak after 30 years and I gotnone of Marc?s helper springs. Throttle closes correctly ever since.

[mlipmd]

Here's a totally different take on that problem. Mine did that twice one day a few years ago- stalled at a traffic light, was able to restart it immediately. Then about a mile down the road, stalled at a stop sign. Restarted it again immediately. Rode home absolutely fine for 5 miles without missing a beat. My fuel gauge read a little less than a quarter of a tank, but I put gas in it from a can at home and it ran fine again. Went to a gas station and filled it up and it confirmed my suspicion that I had run out of gas and my gauge was off and misleading me. Since I cleaned off the sensor and use Techron in my tank every once in a while I have not had that problem again. And always take a look at your trip indicator when your gauge reads low to see how far you've gone on the tank. The mileage indicator is very likely more accurate than your gas gauge on the dash.

[rufcar]

with a bunch of old cars I always make sure the gauge works. I also top off every time I drive but nice call though. Tkx

[1991 Corvette ZR-1]

Another item to consider is the MAP sensor, which is on the back of the plenum. It has a plastic hard line that attaches from it to the back of the plenum to read vacuum. These cars do a decent job at keeping the plenum pretty wet with oil. What can happen is oil gets in that line and obstructs the sensors ability to read vacuum.

Also possible that if the plenum has ever been off, that hard line was compromised. So what some will do is just use a rubber hose to attach to the plenum and the sensor. That was the case on mine. Literally the first time out driving the car and it stalled out at a light. I eventually found a replacement rubber hose on the plenum to the MAP sensor and the line was compromised from the oil soaking through it. Replaced with an actual hard line from Jerry?s Gaskets and the stalling problem was gone. It always happened when coming off the gas and on the brakes a little to make a turn. Car would always die mid turn.

[rufcar]

Interesting. The plenum was off earlier this year by a qualified tech in order to install the correct ac compressor. He also found one of the tabs bent by the PO's tech and the wrong gasket. Now it is all correct but I will check that hard line. Tkx