Bucking At Low Rpm Driving

[broncojunkie]

I recently did some upgrades to my 88gt. 5.0 with some old (1968 iirc) closed-chamber ported heads that were redone with fresh valve job, maf swap, 24 lb injectors with matching maf, explorer intake, 70mm throttle body and spacer, b303 cam, 1.7 roller rockers, rebuilt t5, new heavy duty oem clutch and flywheel, aluminum driveshaft, 3.55 gear.

It idles fine. No vacuum leaks. New iac and new properly-adjusted tps. It has plenty of power and throttle response is great. My problem is that when cruising along at low rpm (say, 1500), the car wants to buck. Is this a problem or am I just experiencing driveability issues due to the cam and other upgrades? I know the B303 isn't too radical, although the lift is increased with the 1.7 rockers. I always presumed driveability issues were typically due to longer duration.

 

[DSB88GT]

EGR valve functioning properly?

Have you run codes?

 

[broncojunkie]

Egr delete and I should check codes again. I'll do it this evening.

 

[broncojunkie]

I was previously getting lean codes iirc, due to fighting some vacuum leaks that caused surging idle problems, but I've since got those all taken care of. Idling fine now and vacuum leaks fixed.

 

[deathb4dismount]

what brand is the iac?

 

[broncojunkie]

It's a parts store brand...autozone I think. Idle is smooth...no surging whatsoever.

 

[broncojunkie]

When I say it "bucks", it doesn't really feel like a miss and rpms don't bounce up and down. If you've ever been, say, in 3rd gear and you try to come to a stop without pushing in the clutch or down shifting, that's what it feels like.

 

[deathb4dismount]

IAC might be sticking at low rpm, and you may not have an issue under throttle. I have had poor luck with parts store brands, highly recommend ponying up the $30 extra for the motorcraft one.

 

[jrichker]

I was previously getting lean codes iirc, due to fighting some vacuum leaks that caused surging idle problems, but I've since got those all taken care of. Idling fine now and vacuum leaks fixed.

No code 11 (two flashes when the computer dumps the codes)? A perfectly functioning system will always get a code 11, it is the everything is OK code. The 11 code is computer passed its internal self test.
If you don't get an 11, you have computer or wiring problems.
Please check and repost.

 

[a91what]

I run the e303 cam and I can say even though it's a mild cam it does not like to run under 1500rpm under load. At 1200 I experience the bucking you are, this is not a tunable issue the fact is it's a byproduct of an ancient cam.