AO

I second the idea of a leak. If there is unmetered air getting in, the ISV will try to compensate for it, but it usually over compensates, so then it kicks back in... this back and forth ultimately causes the surging. I had that happen to me.

Another idea if you have an air compressor is to get a 3" (or-so) PVC cap and tap it to accept a quick disconnect. Disconnect the hose from your SCer and hook this contraption in and pressurize the intake to about 10~15 psi. If you have a leak, you'll hear it and should be able to locate it.

Tampa 928s

This seems like a fuel issue:
Spoke to Tim:
I'm going to check the fuel pressure regulator to see if the diaphragm let go, disconnect the A/F meter to make sure it's not causing an issue finally fuel pressure to see if it dips upon throttle up from a static 38 .

Tampa 928s

It idles fine, not an issue with that, when I accelerate lightly it shows a minor surge, with heavy acceleration it is more pronounced but not really bad. The A/F meter goes completely lean, seems like a loss of fuel pressure.

Tampa 928s

I did spray with carb cleaner around all the rubber boots on intake, S/C hoses and TB no change in idle.

AO

Starting fluid works bit better IMHO...

Do you have a fuel pressure gauge on the fuel rail? If so, try (I know this is hard) putting a camera on it and recreate the symptoms. If it's fuel, this may help to diagnose it.

Can you pressurize the system like I described above?

Tampa 928s

I can mock something up, I have a used air pressure test rig from my Grand National. I could do the redneck thing take the hood off have someone lay on the motor but I don't have a distributor to turn so they may not agree to watch a gauge. Do you have an old camera I can borrow with no deposit.
I'll know a little more tomorrow, the odd thing it idles great It must be something minor, now to find it

Vlocity

Tampa:

Are you using a fuel management unit in addition to a rising rate pressure regulator?

If so it sounds to me like your FMU is not seeing the boost; IE vacum line hooked up incorrectly or the fuel lines in and out of the FMU are reversed.

Ken

Tampa 928s

Yes I do have FMU, the vacuum line t's off of the FPR which is on the passenger side the opposite of what the manual shows. The bottom line goes to the firewall and top goes to FPR.

Jim R.

Mark,

Leave the stock chips in, don't add another variable into the mix now.

Looking at some of the '85-'86.5 pictures floating around, I would double check all the connections between the MAF and the intake plenum. It is possible that one of the hoses has blown off or just pushed back from the "J" and the air metering is thrown way off. When I blew off my MAF connector I could drive it but had some nasty surging.

Also, is the BOV functioning? At idle is there a good stream of air coming out of it? Just make sure it has a good vacuum source and is functioning properly.

A couple of more ideas:

WOT switch not functioning.....I'm not sure where or if the '85-'86.5 have these, but when mine was bad the A/F was erratic and idle/partial throttle surging was nasty.

pull fuel damper vacuum lines to check for fuel leaks.

how old is the MAF? Any restrictors/reducers inside? (if it is old and never rebuilt, I have a spare from my car I could lend you for testing )

Jim

Vlocity

Could you post a pick of your FMU......if it is adjustable, you need to raise your fuel pressure seen under boost. Most have a "Rate of Increase" adjustment and an overall Pressure increase adjustment.

It just sounds like your tune if off and you are lean......I would also plug together the low octane loop which will take 3 degrees of timing out for now until you get this solved. There are no knock sensors and you WILL damage the engine running it full lean under accerlation.

Ken

hacker-pschorr

Not adjustable without taking the top off and changing discs.

Tim and I played around with the adjustable ones. Not necessary and IMO do not work very well.

Vlocity

Hacker:

OK......I understand. Still sounds like its not responding as it should. Can the vacuum source or fuel line routing be screwed up?

Ken

Tampa 928s

I will check the BOV, you say at idle I should feel air from It ?
All the Vac lines are new and good, Octane loop is connected and stock chips are in, got these from Firemed. One caveat I dropped the Maf while working on the car and Boot came off on the first test wondering if this is an issue. Car ran perfect until I added the S/C I'm going to do some testing this afternoon. I have a water leak somewhere from the street or under my house and I need to fit some vales in to test the pressure what a pain so the car will sit until thats done, my water bill went from $13.00 to $200.00.

AO

A screwed up MAF could also cause your symptoms, but I would think you'd experience it at idle too.

BTW, my water bill is typically about $250/mo. during the summer. Not so much during the winter as I don't usually water the lawn in January.

Vlocity

That can't be good.

Do you have someone close by that you can swap out the MAF with.

Hang in there .....the boost is worth it. Honest.

Ken