I've got an '89 IROC, with LB9 and T-5, and 9,200 miles. I've just replaced the Multec injectors with a flow matched set of Bosch's.

Runs good but, if I let it coast at low engine speeds, (like around 1400 or below) and I don't depress the clutch pedal...I get alot of bucking and jerking. It feels like monster driveline lash.

If I depress the clutch pedal....no problem.

Anyone have any thoughts?

PS....Plenum was also ported during injector swap.

 

ttt

 

It sounds normal to me. My LB9 with T5 used to do the same thing in first gear at lower rpms. Your car only has 9200!!!??? miles on it, good find...

 

At what rpms?

 

Oh boy...its been a while. I think at about the RPM range you mentioned. When I would approach a stop light or sign, I used to like to downshift and only use my brakes when I had to. When rolling in first it would start to buck when the RPMs were low, if I didn't take it out of gear or push the clutch it would stall the engine. I am not sure if this is the same situation as you are describing. As for driveline lash, there is always going to be some movement of parts, but that should of course be limited as much a possible. Worn ujoints would probably pose the most common cause of unwanted play in the driveline. Worn engine and trans mounts would be next I guess...

Hope you figure out your ailment...

 

Thanks 92zzzz.

I think that we may be describing the same condition. I've owned my car since new, and it would always "buck"if I lugged it at too low an RPM.

I've just replaced the Multec injectors with a set of flow matched 19 lbs Bosch's....and it seems to start bucking at a higher rpm now.

I called TPIS (which is where I purchased the injectors), and they theorize that the new injectors are a bit richer than stock, causing the earlier bucking.

I'm not really sure that I buy that though.

 

LB9, is that 305, or 350? Did you reset your idle air? Reconnect all connectors securely?

 

Yeah, I think I'll go and recheck my IAC and TPS.....I just don't know if that would make a difference though.

LB9=305.

 

THe rich condition causing a bucking sensation sounds good to me since I know when I had the 305 in there it always ran a bit on the rich side.