IcemanG17

So I took Sean’s 87 s4 5 speed for a run today after a much needed bath. Poor girl was filthy from too much time in storage-shops. Ran fine cold.....once fully warm ran fine while driving, but had an issue at idle and low engine speeds.

The idle would surge, not hold steady. So I’m thinking dirty ISV...no big. Then I noticed having the AC on and max fan was dragging the voltage down to under 12 at longer idle stop lights. As the voltage dropped the idle would get worse and nearly stall....that’s when the throttle response would get extremely sluggish, even decent amounts of throttle wouldn’t bring idle up.....then it would rev quick. Very sluggish. So I think time for an Italian tune up and watch for color out exhaust....after a brief sluggish bit pulls hard to redline in 1st and 2nd...no noticeable color out exhaust.

The 5 speed 928 revs much quicker than my auto did in neutral ..which makes senses considering the weight of flywheel-torque tube is permanent on autos.....this car has no catalytic converters, only an x pipe with 87 s4 rear mid muffler and rmb...so it’s loud but sounds great. I like going under freeway and give it some beans...sounds great

IcemanG17

For some reason I couldn’t finish post so here it is

my thoughts are need new isv or good cleaning. After that is to determine if it’s spark or fuel related. I remember my 88s4 had odd fuel issues from a dying fuel pump when warm, given how long this one sat it’s possible...also fuel is new and fresh just filled her up.

Thoughts?

Mrmerlin

first thing i would do is clean the battery terminals,and grounds
and charge the battery then test it.
Next is swap in a good MAF disconnect the battery to reset the computers

IcemanG17

Thanks Stan
does anyone have a known good MAF I could borrow for test? The battery is new, but car has bad drains so I installed a full kill switch through remote to keep battery alive when parked......

worf928

What Stan wrote and ...

... when the volts drop below 12 funny $h1+ will happen. Time to read-up on alternator threads. It might be something easy like a loose belt. Maybe the nut on the exciter or main power lug is loose. Might be a dying alternator.

Given "too much time in storage-shops" this could be your problem:

worf928

How long does it take, sitting, to kill a fully-charged battery? If the answer is less than a day or two then that's a serious problem and may be related to what you're seeing on the road. If the answer is less than a day, then you have a drain that might be capable of starting a fire.

The Forgotten On

Sounds like failing ignition final stages to me. My 89 had a similar issue. Ran fine for a bit then one of them would act up and half of the cylinders would die causing a **** idle and super sluggish performance.

Restarting it would restore it back to running on all 8 cylinders for a bit or sometimes it would sort itself on its own.

I replaced both and have had no issues since with the ignition system.

Richard S

Yo, Brian! Long time, no see! How's it going?

You can borrow my MAF, it was rebuilt not too long ago. Engine is out (needs a new headgasket), so the MAF is ready to go.

Let me know if/when you need it.

Rich

Jason89s4

I'm doubling-down on the previous comments on electrical. Getting below 12v screws with LOTS of things.
Clean grounds and connectors. I mean really set aside some time and clean your grounds and connectors. What I'm trying to say is, go inspect and clean your grounds and connections.
Also your (+) contacts at your battery and jump post.
Fully, fully charged battery, at least 12.5 volts at the battery, and 12 volts at the jump post. If not, keep inspecting and cleaning.
When running, you should get 12.7 volts or more at your jump post... otherwise check your alternator.
And find the voltage drains! If is that bad (so much that it is draining your battery at rest, and straining your alternator at idle with the AC on), it is not only annoying but dangerous. Can be the sole explanation for what you described.
If you feel like throwing money at your problem, throw $90 at this Optima 400 Charger. It will pay for itself many times over in reviving batteries, conditioning and maintaining them. Slow but very smart.
https://www.optimabatteries.com/en-us/battery-charger Available on Amazingzone.
Jason

polecat702

Brian, you need to get another shark. You've been missed! Are ya still on the job? I miss my life of crime!!! LOL