Have 88 corvette [64K miles] Just had to replace Mass Air Flow sensor. Car runs good at speed[60 to 120] At idle and running at 35 or a little less, car running a little rough. Reving engine in neutral creates backfiring as does driving at 35 or 40 I hear some backfiring also. Need some help.........

Is the service engine light on? Sounds like an emission (egr valve), intake/plenum/runner leak, or timing problem. Have you recently added any parts, or had other major work done? When is the last time it had a tune-up? Need more info please.

Is it backfiring out of the intake or exhaust? If it's backfiring out of either, I suspect you either have a timing problem or you have carbon tracking on your Optispark's cap.

Is the service engine light on? Sounds like an emission (egr valve), intake/plenum/runner leak, or timing problem. Have you recently added any parts, or had other major work done? When is the last time it had a tune-up? Need more info please.
Thanks for the help, no new parts, last tune up 4K miles ago. Back fire is in the exhaust. Service engine light is not on.......do you think fouled plugs possible?

Is it backfiring out of the intake or exhaust? If it's backfiring out of either, I suspect you either have a timing problem or you have carbon tracking on your Optispark's cap.
In the exhaust, thanks for the reply

In the exhaust, thanks for the reply


When is it backfiring out of the exhaust? All the time or just an occasional little pop? Is it a little pop now and then or a KABOOM? And does it pop at idle only? Or only when you lay on the throttle? Or under deceleration only? And did it just start or has it been doing it for a long time? Does the car otherwise run good? Run smooth?

When is it backfiring out of the exhaust? All the time or just an occasional little pop? Is it a little pop now and then or a KABOOM? And does it pop at idle only? Or only when you lay on the throttle? Or under deceleration only? And did it just start or has it been doing it for a long time? Does the car otherwise run good? Run smooth?
It does pop a little at idol, when you rev it up it pops, when driving at 35 to 40 I hear small pops, no big bangs at all. It is a constant. At higher speeds[55 to 75+ I can't hear it but my mufflers are pretty loud[Borla] and probably couldn't hear it anyway. Does run smooth at high speed.

Forgot to mention this problem just started about a week ago

Is it backfiring out of the intake or exhaust? If it's backfiring out of either, I suspect you either have a timing problem or you have carbon tracking on your Optispark's cap.

There is no optispark on an '88

Is your entire exhaust replaced? Do you have headers on it? If you have an aftermarket exhaust, likely you have a leak somewhere.

Thanks for the help, no new parts, last tune up 4K miles ago. Back fire is in the exhaust. Service engine light is not on.......do you think fouled plugs possible?

Weren't the plugs replaced during the last tune up? Also, check around and make sure none of the emission hoses are completely shot, disconnected, or otherwise, especially the ones that run under the plenum to the egr solenoid and egr valve itself. You may have to use a mirror and a flashlight to see under the plenum.

Is the popping sound coming from the rear of the exhaust or somewhere else underneath?

Is your entire exhaust replaced? Do you have headers on it? If you have an aftermarket exhaust, likely you have a leak somewhere.
Entire exhaust was done years ago....... I'll check it closely, but it does run a little rough at 30 to 40mph so don't think it's the problem but will give it a look, thanks again for the input.

sound coming from rear exhaust[plugs done during tune up]

I'm wondering if you have a bad maf control relay, or maf burn-off relay that didn't get caught at the time the sensor was replaced. Both relays are side by side on the firewall behind the battery, underneath the brake booster. You might try jiggling the wires and see if it goes away in case its a loose connection. The burn-off relay, especially, will cause backfiring.

I replaced mine recently due to a code 36. Using a tester confirmed it was toast. Mine had the same backfire issue. I also had a leaking intake manifold gasket too, which can also cause a backfire, or popping noise. Do you hear any hissing coming from the top end of the motor when it idles or you press on the accelerator?

I'm wondering if you have a bad maf control relay, or maf burn-off relay that didn't get caught at the time the sensor was replaced. Both relays are side by side on the firewall behind the battery, underneath the brake booster. You might try jiggling the wires and see if it goes away in case its a loose connection. The burn-off relay, especially, will cause backfiring.

I replaced mine recently due to a code 36. Using a tester confirmed it was toast. Mine had the same backfire issue. I also had a leaking intake manifold gasket too, which can also cause a backfire, or popping noise. Do you hear any hissing coming from the top end of the motor when it idles or you press on the accelerator?
Thanks again Rob, am going to check your suggestions and will let you know the results..........any other thoughts let me know

Keep us posted on it bro.:rockon6rk:

ERG valve seems to have been the problem..........have a new post......if you have a chance take a look. Thanks

ERG valve seems to have been the problem..........have a new post......if you have a chance take a look. Thanks

:thumbsup::thumbsup: