Have 1995 Z28 with stock engine except for K&N cold air intake duct and AEM filter. Car was at dealer for over 3 weeks and had Optispark, Ignition Control Module, and spark plugs replaced. Since then the car has started, but is rough running on cold starts with what feels like a miss. However there is no gas smell. Seems to be the fuel injectors not always being triggered. OBD1 oxygen sensor has lower values on the right bank after cold start than left bank. Runs rough until shut off. Roughness does lessen as one drives. Stop and let car heat soak for 15 minutes or more and start up and every thing is fine. OBD1 oxygen sensor readings are very close to each other on both banks after hot start and drive. Can drive it rest of day if not fully cooled down and will run fine. Let set over night or for extended period and it cold starts and runs rough again. Really puzzled.

 

Any codes coming on?

If the car runs fine when it's warm I wouldn't think it would be a fuel injector. Seems to be a closed loop issue IMO. Have you verified your temperature sensor is working properly?

 

Since you seem to have a scanner, what does the computer think the coolant temperature is cold V hot?

 

The readings I have taken after both cold and hot starts are after vehicle has been driven long enough to get up to operating temp. Ranges from 161 to 194 degrees. This agrees with the gauge at time of scan. Have also taken a scan with vehicle fully cooled down in morning, not started and it scanned at garage temp. They would seem to be correct for length of drive and speed being driven. Also, have never gotten a trouble code on scanner or a check engine light on the dash. Have checked the injectors with a stethoscope and they all "click" with same sound and volume. Also, checked out 6 of 8 with ohm meter and resistance was 12.6 to 12.7 ohms. Within norm of 11 to 14 ohms. Will have to remove some junk to check last two. But agree that if it runs fine when hot started, the injectors should be OK.

 

I would probably start by checking intake seals. Shoot some carb cleaner on the left and right bank intake seals and see if that effects your idle any. Also, unplug your mass air flow sensor and see if that changes the idle any.

Just let you know these are shots in the dark, kind of.

 

Appreciate reply. Not sure about spraying cleaner on left and right intakes. 95 Camaro has only one duct going from intake behind driver side headlights to MAF and only one curved duct from MAF to throttle body. It all seems tight. I think MAF is OK. It is throwing no trouble codes, had been cleaned and get scan readings that look OK - as follows:
Road slow lvl accel lvl lvl lvl I240
accel decel on ramp I40 I40 2lane lvl
MPH 58 61 63 62 60 44 63
RPM 1475 1525 1525 1550 1500 1475 1575
T angle 17 0 21 20 23 17 21
MAP 31 9 37 34 39 30 36
gr/s

Probably could have a cleared logging of activity, ie: level road, accelerating, de-accelerating, etc. However throttle angle and MAP seem to track and indicate to some degree if on or off accelerator or not.

 

No, sorry I meant spray it between the intake manifold and the head. I was insinuating that your manifold gasket is leaking, not the plastic intake. Just thinking maybe you have a seal leaking when its cold then sealing up as it gets warmer.

As for the MAF and MAP, it has been a while since I've looked at common numbers. I do know that you can simply unplug the MAF to test it though. Doesn't cost anything to test, even though that may not be your problem.

Also, maybe check and see if you hear any exhaust leaks.

 

Cold started car and had the same bumpy idle. Disconnected the MAF while idling. Revs came up, but still with the same relative lumpy run, only more frequent due to increased revs. It then slowed back to normal idle, still lumpy. Plugged MAF back in and it retained regular idle revs and lumpy running.
Also, checked the last two injectors and had 12.6 ohms - that makes all 8 being within the 11 to 14 ohm range. 7 at 12.6 and 1 at 12.7.
Checked for leaks in the intake, no change, guess it's tight.

 

If the MAP readings are in kPa, they look low. You should see about 35kPa at closed throttle idle, and MAP should increase with opening throttle angle, approaching barometric pressure (~100kPA if you are at sea level) at wide open throttle (WOT). The "9" is a decel number, and that looks low too.

 

Do you still have your air pump?

Have you changed the O2's in the last 60K miles?

 

OOPs. Sorry. Those were MAF values in gr/s. Added MAP in volts. Also, added O2 sensors. Have the OBD1 readings on a spreadsheet, but it doesn't seem to copy well into this forum.

Road slow lvl accel lvl lvl lvl I240
accel decel on ramp I40 I40 2lane lvl
MPH 58 61 63 62 60 44 63
RPM 1475 1525 1575 1550 1500 1475 1575
T angle 17 0 21 20 23 17 21
MAF 31 9 37 34 39 30 36
gr/s
MAP 2.74 0.62 2.2 2.88 3.25 2.58
volts
O2 L 761 4 61 268 761 664 374
mVolt
O2 R 805 4 783 783726 712 70
mVolt

I think the O2 sensors have been in since factory. Tried to remove the driver side sensor and it seems to be "rust-welded" in place. The passenger side is very difficult to see, let alone get at to remove. How does one replace them? When I pulled the plug on the MAS it did throw a trouble code indicating a failed MAS. The air pump is in place and would assume to be running.

 

What are you scanning it with? If you have a file, either put it on an FTP site, or e-mail it, prefereably in .csv format. It's too difficult to work with what you are posting. I tried indexing it with hyphens but its a pain.

Individual frames are not really useful. You need a time reference and a continuous scan.

 

I'd put O2's in it. Use a 7/8 wrench. Or buy an O2 socket.

See if the air pump comes on at cold start. If not it could account for what seems to be a long warm up.

 

Replacing the O2's sounded easy enough. I had the stock headers on the garage floor and used a sledge hammer to break them free. They would have been nearly impossible to get out on the car. That is after heating them up to help break them loose. Since the dealer did the work previously, I assume you would have them replace the O2's also. JMO

 

Am trying to change O2 sensors my self. Taking car to dealer requires a stop at a bank with a mask and all the cameras now make that risky. Have a special 7/8 inch sensor tool and breaker bar, but couldn't get it to budge. Didn't want to put so much pressure as to damage down pipe. Could only get at driver side sensor. Don't know how to get at passenger side sensor.
In answer to previous question - there are no exhaust system leaks.
I am using an AutoXray EZscan 3000 for the OBD1 scans. I think one can do a series of scans linked to a computer, but I haven't been able to decipher the manual instructions to do that. It may require some additional software I don't have.
What I have accumulated are several scans: engine not running and running: cold and hot: driving and stopped: accelerating and de-accelerating. Trying to find some thing that after cold start and hot start that are at variance in the same operating mode (speed, acceleration, de-acceleration, etc.).
The car is warming up in what seems to be the normal length of time. The strange thing is that on cold start the lumping continues for long after it has reached normal operating temp and doesn't stop until it has been shut off and allowed to "heat soak" for 10 to 15 minutes or more. After the "heat soak" hot start it runs normal. Once it has been heat soaked, it will run normal after each stop there after. The car has to be completely cooled down to begin the "cold start lumping".
How do you determine if the air pump is running or not?
Appreciate the input. This seems to not be an uncommon problem with these cars, but seem to be endless reasons for it.