Low RPM roughness

[Reid Bishop <rbish@ibm.net>]

I recently completed a Jeep conversion, placing an 89 4.3 TBI & 700R4 into a
Jeep Cherokee.  I used a Howell Harness, a '7747 ECM, and stock 4.3 EPROM
image (AKDX2088).  This engine was completely rebuilt, bored .030 over, and
I installed an Edlebrock Performer manifold, Edlebrock Performer CAM (fairly
mild roller cam, but definitely not stock), Edlebrock Roller timing chain,
and roller rockers.  O2 is mounted on the Y-Pipe, just below the drivers
side manifold collector (stock location on an S10 I believe...), and stock
S10 manifolds were used.  Exhaust is 2.5 inch all the way back, with a
high-flow cat and a FlowMaster muffler.

After about 800 miles, the engine runs fairly good, but still has a few
problems.  It idles very smooth, but does tend to hunt about 100 RPM when it
is warmed up to 195F.  It also runs very rough just off idle- anywhere
between 750RPM and 1800RPM it just can't seem to keep from stumbling all
over the place.  ECM never sets a code, and I have been having trouble
getting stable ALDL data when the motor is running.  Timing is set to 6
degrees BTC with the ECM control disconnected.  The ECM goes into
Closed-Loop after 1-2 minutes after a cold start.

Any idea what to look for when hunting this problem down?  Fuel Pressure is
dead nuts at 13PSI after I switched my fuel return line to a 3/8ths line.  I
don't detect any vacuum leaks, but I wonder what the stock vacuum reading
should be on this engine?  Again, it idles great aside from a minimal hunt,
but immediately off idle is where it starts to get unhappy.

Also, this combo gets terrible mileage right now- I didn't expect good
mileage, but I am running 14.5MPG right now, no matter how I drive it.  I
have 4.55 gears, with 32 inch tires, with a corrected speedo gear- this
'appears' as something like a 4.11 ratio.

I don't have the Edlebrock chip yet for this manifold/cam combo- so maybe
that's the problem, but I would not expect to see it have problems at these
low RPM's.

Any techies have a suggestion?

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