TealZR1

My 91 ZR1 runs somewhat rough until I run it a few blocks and heats up a bit - it than runs well after that. Any ideas on where to isolate what the problem could be? Thanks in advance

Dominic Sorresso

Did anything change at the time the car started to run rough?

Rkreigh

start with basics

how are the injectors, map? put the car on a scanner

for sure the factory manual is your best guide here

I have one for sale cheap if you need it

how 30 plus the ride sound?

Dominic Sorresso

Do u have a WB O2 available? Did the rough startup begin after some other mod or change to the motor. Does it start rough in a warm start or just when motor is cold? Have u noted what the coolant temp is when it starts to smooth out?

TealZR1

Thanks to all that responded to my question.

The only "mod" just recently was I had Haibeck Automotive service the Throttle Body and I installed it back on last week when the rough drive occurs until it warms up.

I have double and triple checked all connections. I would not think the TB has anything to do with this.

I will go through all your suggestions.

Thanks!

Paul Workman

Initially, I wuz going to see what result you got conducting a fuel pressure test:

Switch on, pumps come on for a second and switch back off. Pressure = mid 40s. THEN...watch the pressure for 5-10 minutes. Pressure should not drop more than a pound or two, as long as the injectors are not leaking, nor the fuel check valves (in the pumps).

I'd also be curious too how the plugs looked if the engine were shut off before the idle smoothed out.

Then, I'd like to know what the IAC voltage is at idle, and what the IAC counts are?

A scanner and the FSM would be invaluable about now!

FASTAZU

I have a scanner that will log everything on the fly, maybe we can arrange to meet some time and check things out, I'm about 30 miles south of Atlanta just off I75.

billschroeder5842

You might want to double check you IAC as it sits in your TB. If your TB was serviced, the IAC may have been damaged and/or not seated correctly. If you IAC is jacked, you will have idle issues until it warms.

Who knows.

BTW... please consider a Haibeck chip. Well worth the money.

TealZR1

Thanks Bill will check out the IAC. I did get a Haibeck chip a while back and well worth it. Thanks Again

Paul Workman

Curious... How'd the IAC check out? My wife's IAC counts were off quite a bit, and the voltage wasn't that bad, but "off" as well.

Setting the voltage was easy enough, but it took me a while to realize that after adjusting the idle air screw, the ignition had to be turned OFF for about 10-15 seconds before restarting the motor to check the affect the screw adjustment had on the IAC counts. And, of course adjustments to the screw directly affects the (edit) TB voltage.

So, tweak the screw, turn switch on and set the IAC voltage, and then fire it up and check the IAC counts to see what affect the screw adjustment had.

I set Ami's TEAL ZR-1 at 8 counts and the TB to 0.54volts and the issue with stalling on startup and also when coming to a stop w/ the AC running - both went away.

FYI For anyone interested, the "taped" wrench is securing the set screw while the jam nut is being attended to.

The 5 step count reflects the IAC with the motor idling and fully warmed up with the AC turned off. The "24" step couts reflects the IAC counts when the AC compressor was activated.

TealZR1

thanks Paul, I changed out the IAC valve and told it was a plug and play with not additional adjustments. Are you saying it needs to be adjusted with the help of a scanner?

looks like I will need to invest in a scanner with this car. Thanks Again\ and let me know!

Regards

Paul Workman

Yes, the IAC IS plug and play.

Just to be clear, the adjustment idle air screw AND the idle voltage are BOTH on the throttle body. (Accidently said IAC when I meant THROTTLE BODY. See correction.)

Yes, a scanner (or the like) is needed to verify IAC counts. Worth every penny!

TealZR1

Thanks Paul, one thing I noticed today after isolating the issue is this:

The car starts as it should and idles down to 750rpm and purrs like a kitten. When it reaches temperature about 120 degrees it starts to bog down (rough idle) a bit but does not quite stall. after about 60 seconds and it gets hotter it than smooths back out and good from there!
Any suggestions? And what brand scanner to you suggest? Thanks for your help!

Demps

O2 sensors

Ted



I can do better: watch for transition from open to closed loop if you have a scanner attached. I'll bet your rough running window is coincidental.

FASTAZU

Offered many posts back...you can lead a horse to water but you can't make him drink

74 LS4-454

I can give you a first hand update on Mike's (TealZR1) ZR-1. Mike contacted me some time ago after reading my TB Thread on the Registry, about his problem. I didn't know if I would be able to help him out, we had multiple conversations and I offered to ship down to him my Tech 1 ( which he finally agreed to) so he could get some readings. After he received the TB back from Marc, upon installation a huge coolant leak developed which was coming from the TB-Plenum connection that was not properly tighten. Therefore what I thought and after consulting with another LT5 owner, it was determined that the O2 sensors (which Ted mentioned) were now contaminated. That is when his problem started with the rough idle occurring between 110*-123* and going from open loop to closed loop and then returning to open loop and staying there, even when fully warmed up.
He did attempt to get the sensors replaced, but ran into problems with the connectors due to them being changed most likely when the PO put headers on the car. He is supposed to get that corrected the last time I spoke with him.
I'm walked him through the Tech 1 to get readings and we found that his IAC counts were "0" @idle and would only go to a certain count when driving the vehicle. That problem was very similar to what I experienced earlier this year with my Z. We were in the process of adjusting the idle screw, (which did not take place) as my Tech 1 was not responding all of the time due to an intermittent problem which turned out to be a broken wire inside the connector, which I soldered when the Tech 1 was returned to me.
We also reset the IAC with the unit he already had in the car and a replacement which he wanted to try out. It had no effect on the IAC's, which I thought it wouldn't. Again similar to my previous problem.
So there was more than one problem which needed to be addressed. As of this date, Mike's status may be the same until the O2 sensors get replaced. And then he will need a scanner so he can adjust the TPS and idle screw to hopefully get the IAC's in spec.
I don't think he comes on the forum that much, so now you have an update about the condition of his LT5.....

Merry Christmas everyone....enjoy and safe travels.......

Tom

Paul Workman

THANKS, Tom.
Not everyone gets the opportunity to experience how coolant affects their O2s. Not everyone would make the connection between the two, especially w/o a scanner.

Merry Christmas to you and yours as well!

74 LS4-454

Thanks Paul........also glad to update Mike's status ......I think once he gets the 02's replaced and the IAC's in spec...he will be very satisfied......

Hope that Santa brings you and Ami some ZR-1 goodies.....
We are looking forward to our Christmas Eve get together with the family tonight....as we do the seven fishes and other food items as well.....my favorite Holiday......lol

Have fun and enjoy!!!!

Tom