OBD1 Fuel Trim

**Shudson105** · 03-19-2009, 04:11 PM

I have a 93 Firebird Formula (LT1)(80k miles) which just recently began exhibiting surging during idle. This surging only happens after the engine reaches operating temperature. Also, a few weeks after that started (and after I just cleaned my SLP air filters) the car seems to lightly shudder while under hard acceleration (it feels like I am accelerating over a wavy road).

When I hook up a scan tool, I have no trouble codes. I do however see that my short term and long term fuel trims are different between the left and right banks. For example, while the engine is at oper temp and closed loop, my short term fuel trim is 70 on left side and 130 on right side. The long term is 118 on left side and 125 on right side. These are averaged over 1min while at idle.

What does this mean and does it have anything to do with my two problems?

Appreciate any input you may have.
Steve

**mark21742** · 03-20-2009, 01:00 AM

your fuel trims sound WAY off and that by itself can give you problems like your talking about.
what shape are your o2 sensors in, do you have any mods and have you had it tuned?
plus check your intake tube between the MAF and tb for any leaks/cracks.
bad o2 sensor or bad signal from the MAF would really throw your fuel trims off.
I can't give much more help, I haven't work on many ODB1 systems

**Orcus79** · 03-20-2009, 07:04 AM

I would start with fresh 02s,as they are probably dirty and have drifted out of range, but not out right failed. And the next would be to go over the intake system, could also be an intake gasket has let go.

**Shudson105** · 03-20-2009, 07:22 AM

I have no cat and as far as I know, the single o2 sensor is still original (at 80k miles). The intake system from the air filters to the tb is solid and no leaks. I don't have a MAF since its an LT1 from 1993...just MAP sensor on the intake manifold. If the intake manifold gasket has formed leaks, how would I check for that?