Rough Idle/Hesitation/Backfire

[Gary Yarbrough]

I'm hoping for some help with my 90 ZR-1. It idles just a little rough (not too bad), but it really hesitates if I floor it from idle. It will also sometimes backfire. If I smoothly and slowly give it the gas or start from about 2500 RPM, it is fine.

Things I've checked:
MAP hose is fine.
No vacuum leak (well...I've got the usual very slow leak).
Plugs & Wires are ~1 year old with ~5,000 miles.
Injectors are Accel with about 3,000 miles.
I have a chip from Jim VanDorn, otherwise the car is stock.

About two weeks ago, I checked codes because I got a brief SES light while cruising on the free way and had a left oxygen sensor code. I replaced the sensor and that problem seems resolved. I've had this idle issue for a while now and would really like to get it resolved. Any suggestions would be greatly appreciated!

Coil(s)

[XfireZ51]

DVM the TPS sensor. Also, while the car is idling jiggle each of the three wires on the TPS.

[Gary Yarbrough]

Please excuse my ignorance, but what does "DVM" mean?

[DTZ ZR1]

I somewhat of the same problem, changed plugs it was a little better. After I ran it for a minute or two, I took plugs out and one was wet. Put them in started the car and pulled the plug wires off one at a time. When I got to #4 and #7 plugs there was no change in the idle and you did not hear the spark jump either. I am in process of changing them out. Good luck.

DT

[secondchance]

Originally Posted by Gary Yarbrough

Please excuse my ignorance, but what does "DVM" mean?

Digital Volt Meter. I believe you are looking for .54 volts.

[Gary Yarbrough]

Thanks for the suggestions so far. When I pull the plug wires 1 at a time, all of them do make the idle rougher. However, there are some with a very strong loud spark (I can actually see it) and others that seem much weaker. So, I'm thinking I need new coils as suggested. So, I have a related question. Given that the plugs and wires are about 1 year old, should I also replace them when I do the coils or are they most likely okay?

[secondchance]

Originally Posted by Gary Yarbrough

Thanks for the suggestions so far. When I pull the plug wires 1 at a time, all of them do make the idle rougher. However, there are some with a very strong loud spark (I can actually see it) and others that seem much weaker. So, I'm thinking I need new coils as suggested. So, I have a related question. Given that the plugs and wires are about 1 year old, should I also replace them when I do the coils or are they most likely okay?

As for plugs, depends on what was installed and visual inspection. Plugs can easily replaced without pulling the plenum. Visual inspection and replacement if they look bad. I ran AC Delco platinum plugs about 5 years ago. Car ran real bad right after installing them. Upon visual inspection, it turned out one plug had cracked insulation.

If not plugs then pulled the plenum. At that point check wires for resistance. Generally it should should be good for 3-4 years at least.

[Sgreg]

Wires should be fine. Take a close look at each plug to determine whether they need replacing.

[XfireZ51]

Originally Posted by Gary Yarbrough

Thanks for the suggestions so far. When I pull the plug wires 1 at a time, all of them do make the idle rougher. However, there are some with a very strong loud spark (I can actually see it) and others that seem much weaker. So, I'm thinking I need new coils as suggested. So, I have a related question. Given that the plugs and wires are about 1 year old, should I also replace them when I do the coils or are they most likely okay?

If you find that the weak spark comes from a pair of plugs with a common coil,
ie 1-6, 3-2, then that would be a clue on needing coils.