90 ZR-1s and fast idling?

[Paul Workman]

Assuming (otherwise) normal operation, is a 2000 rpm initial idle "normal" for the 90 Zs?

Even after it warms up, I have a fast idle after coming to a stop (sign) after normal (for me and a Z) hwy speeds. If I sit in neutral and let it idle, the idle speed evenually drops to "800 (my tac) after about 15 seconds or so. After that and it will idle normally at a stop light/sign every time. Otherwise, she'll seldom come off of 2k idle w/o first pausing somewhere to let it adjust.

I seem to recall something about this little quirk and the 90s. Is this normal? Does Marc H's have this handled in one of his chips?

Other than that, she runz like 'er azz was on fire!! WHAT A BEAST!

TIA,

P.

[tomtom72]

Paul there is a TSB over at the netreg site about this 'quirk' on the 90's. There was no recall issued. Just an updated EPROM as an answer to what you are describing if the customer made complaints about this condition to the dealer while under warr.

I remember reading the TSB and I bought the updated EPROM back in 05 from a dealer, $40.00, and it almost eliminates the issue. It still 'hangs' a bit but returns to normal much quicker than my original EPROM. There is a thread about it here where one of the guys that are into writting their own EPROM's listed all the changes on the updated EPROM....quite an extensive list of changes & interesting reading.

:thumbsup:
Tom

[32valvZ]

I JUST, as in this week, got my chip back from Haibeck & my 92 is doing pretty much the same as yours Paul. When I start it up it soars to like 2000rpm & hangs there a few seconds. Then also like yours, it seems to hang when coming down from cruising speeds as I approach a stop. I noticed this both before & after the changes Marc made to the prom.:icon_scra

[Aurora40]

My car has only done that when it had leaks. When I bought it, it already had the latest PROM, and I've had Haibeck PROMs since. Mine only idles high when the car is moving, like when slowing to a stop in neutral it will idle around 1000-1200, but drops when the car stops.

If you can scan it, look at what the "desired idle" is and also if the IAC counts come down when you stop. If so, but the idle doesn't drop, it's a vacuum leak. If it doesn't command it down, perhaps you need an updated PROM.

[RedSled]

My '90 will sometimes do the same thing, but doesn't reach 2000rpm. More like 1500-1600. Then it will normally return to a 800-900 idle after 10-15 sec. It has consistently done this for the three years I have had the car.

-Keith '90 Red/Red #1383

[32valvZ]

[QUOTE=Aurora40 Mine only idles high when the car is moving, like when slowing to a stop in neutral it will idle around 1000-1200, but drops when the car stops.

Mine does this exactly. So I guess thats a normal condition.... When it first starts it idles high for 3-10 seconds. It seems kind of excessive though. Its actually around 1600 rpm, not the estimate of 2000 that I mentioned earlier :merror:

[Aurora40]

I think they all rev up a bit on startup, I always thought it was kinda cool. Like it was sleeping, and now it's awake!

[Paul Workman]

I think they all rev up a bit on startup, I always thought it was kinda cool. Like it was sleeping, and now it's awake!

I guess it gets that oil a splashin' up under the pistons right away - a good thing on a cold start, I suppose.

P.

[tccrab]

This has been a pet peeve of mine for a while.
I have a Haibec prom and the idle is much better than the original factory prom.
When I start the car she idles fine.
After I drive it a little while and roll up to a light sometimes the idle does not return to 600, it seems to hang at 1000-1200. Sometimes it goes down to 600 after I stop, sometimes it doesn't.
If I tap the gas slightly as I roll to a stop the idle goes down to 600.
I've always thought it was something in the throttle body, maybe gunk or something that doesn't allow the blades to close properly.
I've been afraid of messing with it for fear of f'ing up the magic black goo that seals the throttle plates to the throttle body.
In the good old days of Holly carbs you could spray cleaner down the carb with the engine running and clear gunk off of the throttle plates and stuff.

TomC

[XfireZ51]

This has been a pet peeve of mine for a while.
I have a Haibec prom and the idle is much better than the original factory prom.
When I start the car she idles fine.
After I drive it a little while and roll up to a light sometimes the idle does not return to 600, it seems to hang at 1000-1200. Sometimes it goes down to 600 after I stop, sometimes it doesn't.
If I tap the gas slightly as I roll to a stop the idle goes down to 600.
I've always thought it was something in the throttle body, maybe gunk or something that doesn't allow the blades to close properly.
I've been afraid of messing with it for fear of f'ing up the magic black goo that seals the throttle plates to the throttle body.
In the good old days of Holly carbs you could spray cleaner down the carb with the engine running and clear gunk off of the throttle plates and stuff.

TomC


The high idle on start is an emissions thing to get the cats and O2s lit asap. Same for the high idle under freewheeling. Its emissions. There is a decay delay set in the prom which can be changed.
As for goosing the throttle and idle dropping, I would clean the TB and also the IAC and passage.

[Aurora40]

Be careful cleaning the TB, if you clean the "dag" off the secondary butterflies, you'll probably get a high idle. That's what happened to mine.

[tccrab]

Be careful cleaning the TB, if you clean the "dag" off the secondary butterflies, you'll probably get a high idle. That's what happened to mine.

See, there it is right there.
The "Black Magic Goo" that causes a high idle.
I'm hesitant to spray carb cleaner into the TB for fear of messing this stuff up.

TomC

[tomtom72]

This is just a fwiw on the "dag"......I used STP throttle body cleaner....not carb cleaner...on my T/B when I had my stuff apart and the T/B cleaner didn't do anything to the DAG. I was careful not to aim at it when spraying and I mostly used cotton balls soaked with the stuff to clean up the bores & t-plates by gently wipping till I got all the soot or whatever to come clean. It took a bit of time but was well worth the effort as my T/B came out very clean and the DAG was unharmed.

:mrgreen:
Tom