Stranded - idles fine but doesn't want to rev

caitov · 11-23-2013, 01:26 PM

Hey Guys
Took my 88 3.2 on a nice drive this morning and now went to restart it about one hour later and now it doesn't want to rev.
It starts just fine and idles great. When I give it gas it doesn't want to rev. It mostly stays at idle and then will wildly rev if I push it but then drops nicely back to idle when I release the gas. It just doesn't hold the revs.
Any ideas? It'd be nice to be able to drive home today.
Thanks

Scooter · 11-23-2013, 01:36 PM

Clogged fuel filter maybe.

steely · 11-23-2013, 01:38 PM

You may want to check the linkage from the pedal thru the tunnel to the engine.
Behind the drivers rear tire mounted on the transmission, there is one small bell crank, and there is another bell crank on top of the engine underneath the intake that links to the throttle body.
Check that none of the linkages are loos/disconnected/bent, and that there are 2 springs on the top bell crank.
You could also jump right to the throttle body (TB) and see if manually manipulating it will affect the revs.

If it does, your linkage is disconnected somewhere.
If it does not rev when you flip it at the TB, I don't know (some body else got an idea?).

caitov · 11-23-2013, 01:44 PM

Thanks for the suggestions so far.
Linkage is fine as I can rev on the engine and it's exactly the same issue.
Fuel filter might be more than I can check here.

Any more ideas I can try away from home?
Thanks again.

t6dpilot · t6dpilot's Garage

Had a similar issue with a 3.2 in a 914-6. Turned out to be a clogged fuel filter. But before I found that, I checked the AFM output resistance to make sure it was functioning properly. That is more for the home shop and doesn't help you right now. I would bet impeded fuel flow somehow - tank filter, line blockage, or filter. Doubt it is the pump, could be pressure regulator problems if you have one?

My bet is fuel filter. Get a cheapie from the nearest auto parts store and put that in. Itll getcha home. You do have tools, right? Or call AAA. Carry spares with you as often as you can. Good luck!

newms · 11-23-2013, 03:40 PM

Check the rubber sleeve that connects the two sides of the intake manifold. It's just a hose clamp. I chased an intermittent problem for a year before realizing that I had a vacuum leak at this sleeve. Tightened it down and problem finally gone. My symptoms similar. Idles perfectly go to gas and nothing. Then it would catch and rev. Then die back to idle. Check all vacuum hoses but my problem was just a loose hose clamp. Good luck.

caitov · 11-23-2013, 05:36 PM

Thanks everyone for the suggestions.
I couldn't find a fuel filter locally. I'll have to try again tomorrow. The car's in a safe place - just feel bad it's not here in my garage.

I'll let you know what it ends up being.

Tippy · 11-23-2013, 05:46 PM

Sounds like you have a big vacuum leak somewhere. Many vacuum lines to check. Since it's sudden, I'd imagine a line popped off or cracked.

These engines will idle beautifully at super, super lean conditions. But, once you try to load, it'll lean out as you describe.

Scooter · 11-23-2013, 06:28 PM

You can roadside test the filter by removing it an trying to blow through it. If you get any resistance at all, then it's clogged. At least that is my rule of thumb.

caitov · 12-03-2013, 06:59 AM

In case this can help someone in the future, the problem was finally found. After checking all the obvious like mentioned above, it turned out to be the idle micro-switch.

A simple part that unfortunately took a while to figure out.

GH85Carrera · GH85Carrera's Garage

Quote:

Originally Posted by caitov

In case this can help someone in the future, the problem was finally found. After checking all the obvious like mentioned above, it turned out to be the idle micro-switch.

A simple part that unfortunately took a while to figure out.

Interesting. So a bad idle micro switch allowed it to idle but not run. I would never have guess that.

T77911S · 12-03-2013, 07:32 AM

check for big air leak.

all fuses good

DME relay

caitov · 12-03-2013, 09:16 AM

Quote:

Originally Posted by GH85Carrera

Interesting. So a bad idle micro switch allowed it to idle but not run. I would never have guess that.

Yeah, apparently the switch was stuck in a position that told the ECU it was idling even when pressing the throttle.

At least now I know my fuel filter is good, O2 sensor is fine, no vacuum leaks, .....

GH85Carrera · GH85Carrera's Garage

Quote:

Originally Posted by caitov

Yeah, apparently the switch was stuck in a position that told the ECU it was idling even when pressing the throttle.

At least now I know my fuel filter is good, O2 sensor is fine, no vacuum leaks, .....

HMMMM.

That is even more interesting. So it was stuck in the closed position. So if you just disconnected it completely I presume it would not idle but it would run.

I am just trying to figure if my 911 ever did that if could I just unplug the idle micro switch and drive off.

As Spock would say "Fascinating."

GaryR · GaryR's Garage

Quote:

Originally Posted by GH85Carrera

HMMMM.

That is even more interesting. So it was stuck in the closed position. So if you just disconnected it completely I presume it would not idle but it would run.

I am just trying to figure if my 911 ever did that if could I just unplug the idle micro switch and drive off.

As Spock would say "Fascinating."

C'mon Caitev, be a sport and put the old switch back on, unplug it, and see if that would have got you home!

GH85Carrera · GH85Carrera's Garage

I was just trying to file the info away in my brain. If I am ever in a situation where my 911 will not run but it idles just fine I will sure unplug that switch and see if I can continue home.

GaryR · GaryR's Garage

Quote:

Originally Posted by GH85Carrera

I was just trying to file the info away in my brain. If I am ever in a situation where my 911 will not run but it idles just fine I will sure unplug that switch and see if I can continue home.

I wasn't joking, it would be good to know!!