Deaded Idle Surge?

[vettn71]

This evening I was driving my 90 Z back from the Dallas Auto Show. Everything was golden until I pulled off the highway and up to a stop light. The idle stayed at about 2000 RPM for 20 seconds or so, then, in steps, dropped to 1200, then 750, then 600 or so where it remained for the rest of the drive home (all on secondary streets). It hasn't done this before, but I really haven't driven it enough to know what is normal. Any comments/suggestions? :dontknow:

Jim

[carter200]

Check your vacuum hoses. Usually they are the culprits. One is probably cracked or hanging on by a thread. Good luck and let us know what you find. :handshak:

[XfireZ51]

This evening I was driving my 90 Z back from the Dallas Auto Show. Everything was golden until I pulled off the highway and up to a stop light. The idle stayed at about 2000 RPM for 20 seconds or so, then, in steps, dropped to 1200, then 750, then 600 or so where it remained for the rest of the drive home (all on secondary streets). It hasn't done this before, but I really haven't driven it enough to know what is normal. Any comments/suggestions? :dontknow:

Jim


Check the PCV "F".

[GOLDCYLON]

Aslo are you running the original PROM? Gm released an update to the prom due to this surging problem but the previous owner may or may not have gotten it fixed. If this is the first time you have experienced this then as the other members have already stated the PCV hose and even a dirty IAC can cause this as well. If you had poped a hose under the TB the idle would never fall.

[tomtom72]

Just in case you may want to see the TSB on the PROM update it's over at the netreg site.

http://www.zr1netregistry.com/bulletins/476503-1.jpg


The only issue now is this replacement PROM seems to be NLA. I'm not 100% positive on the NLA, but when I run the P/N nothing comes back. I get the "no such part number" message.

I'd check for vacuum leaks first and you can tell if the PROM was done by hooking up a scanner as it will give the PROM ID# after you verify the VIN #.

:cheers:
Tom

[Jarek5_7]

maybe someone could copy that updated prom and post a file so everyone could burn it because I also know that its no longer availabkle from gm

[XfireZ51]

Here it is. I found a BRXB which looks to be a 91 ZR-1 cal as well. Don't know much about it but maybe some of the ZR-1 gods can chime in.
:cheers:

Note: I make no guarantees for the bin. Use at your own discretion. If somebody tries it out, let us know if it works.

[Sgreg]

maybe someone could copy that updated prom and post a file so everyone could burn it because I also know that its no longer availabkle from gm

This should have been a recall and not just a Service Bulletin ! Hard to find an owner of a 90 or 91 Z with the original Memcal that hasn't had high idle problems and hard hot cranking. :confused:

[vettn71]

I've got a Haibeck (sp) prom in the car. Still have the original in a bag. I haven't had a chance to look at the vacuum hoses and just bought a set of manuals off ebay. I haven't driven the car since bringing it home from the Dallas Auto Show.

Jim

[GOLDCYLON]

Ok that answers that Jim your prom is ruled out as the culprit. So a dirty IAC or a vac hose maybe the issue. Did the car backfire upon a startup recently? Normally that event occurs before the PVC hose blows off behind the plenum next to the firewall. As will cause the idle symptoms

[GOLDCYLON]

This should have been a recall and not just a Service Bulletin ! Hard to find an owner of a 90 or 91 Z with the original Memcal that hasn't had high idle problems and hard hot cranking. :confused:

I agree Greg but at this point with the expection of the 163 mile 90s showing up latley most have replaced the chip already. But I concur it should have been a safety recall. Something tells me if the car was automatic it would have been due to lurching events.

[tomtom72]

Just an observation, the date on the TSB is 2/94. I'll bet there had to have been complaints or something. It seems to have taken quite awhile for the software guys to figure out a soloution; or not too many 90 owners were driving their cars and complaining? :dontknow:

My 90 had 7400 on it and still had the OEM PROM in it, that was my first "Mod".....I should have bought two as cheap as they were from GM. Sheeeish, I'm soooo dumb sometimes. They were like $34.00 each! Now I have to give it up to have Mr. Haibeck redo it when I get my headers installed as he said that is the better of the two programs to write to.

[Jarek5_7]

can anyone see if its a updated bin? what xfire posted?

two days ago when finally weather let me drove the Z, I took a spin. the car runs strong and full power comes on and really pulls great. after cold start rpms go down to reasonable cold engine rpms but after short drive it idles ok but after engine gets warm it idles very high. it makes me MAD, I really think I have no vacuum leak , I checnged injectors, plenum gaskets, tb gaskets, checked vac hooses, put in new pcv valves, new check valves under plenum etc.

while slowing down to stop on neutral it idles around 2k rpms !! and hold it for a while at stop and then starts after 2 sec to drops by steps but not to desired level.

this is the most annoying thing in the car, I will be so happy when I fix it....

[vettn71]

Daryll

The car has never backfired; has always run as smooth as a baby's behind. I know it has the original plugs (15xxx miles), so they probably need to be changed out, but that's a different issue. I'll have to get under there and check all those hoses. Nothings been off, nothing has been changed. ?????

[XfireZ51]

can anyone see if its a updated bin? what xfire posted?

two days ago when finally weather let me drove the Z, I took a spin. the car runs strong and full power comes on and really pulls great. after cold start rpms go down to reasonable cold engine rpms but after short drive it idles ok but after engine gets warm it idles very high. it makes me MAD, I really think I have no vacuum leak , I checnged injectors, plenum gaskets, tb gaskets, checked vac hooses, put in new pcv valves, new check valves under plenum etc.

while slowing down to stop on neutral it idles around 2k rpms !! and hold it for a while at stop and then starts after 2 sec to drops by steps but not to desired level.

this is the most annoying thing in the car, I will be so happy when I fix it....


Jarek,

The bin I posted is an updated one. It uses the AFA Mask ID which is an update to the original AF Mask ID. GM added some code to all the ZR Masks at one point and came out with "A" versions of them. The BFXB won't work well with the AF Mask. I also compared the BFXB v BRXB bin.
They are nearly identical with slight changes in Injector Bias v Battery Volts, and in some of the Knock calibrations. Both also have slightly lower IAC steps v Coolant than the stock bin which is probably part of the fix they incorporated.
You can burn these bins and install, or you could take stock bin and make mods to drop the idle sooner/quicker and not raise it when coolant temps increase.

[tpepmeie]

BRXB is not a factory ZR-1 broadcast code. If it is that close to BFXB, then I suspect somebody has just renamed it. The Mask ID nomenclature ("AFa" vs. "AF", and so on) is not a GM term. Rather, it was coined apparently by TunerCat as a means to differentiate the various versions of a calibration within the same year. The Program ID byte still appears as AF in the calibrations, even though they are different programs.

Todd

[XfireZ51]

BRXB is not a factory ZR-1 broadcast code. If it is that close to BFXB, then I suspect somebody has just renamed it. The Mask ID nomenclature ("AFa" vs. "AF", and so on) is not a GM term. Rather, it was coined apparently by TunerCat as a means to differentiate the various versions of a calibration within the same year. The Program ID byte still appears as AF in the calibrations, even though they are different programs.

Todd

Todd,

Thanks for that clarification. Have you had a chance to verify whether the bin I posted is correct?