maaattholmes

Hey everyone,

Got a weird one, wondering if I might get lucky and somebody could chime in with some insight into this.

So I've had my car for about 2 months and I believe it's done this since I owned it, but at 4000rpm it seems to just not make power, I don't like to rev it past 6000rpm while it's struggling just in case it's going lean but from what I can tell it just falls over at 4000rpm and doesn't recover again, so less of a flat spot and more just a weird lack of power.

It may/may not be related but also has trouble starting sometimes once warm/hot (not overheating, but after spirited driving sometimes). It would just crank and not fire, if I gave it a bit of throttle it would then fire, but tried it again today after it wouldn't start and it wouldn't even start with throttle input, just cranked over.

It's also died while idling twice now, once while driving very slowly over a speed bump (at idle), and the second time today I started it cold and sat outside the car to see what it does as it warms up and pretty much as soon as it got warm it died (quite quickly, didn't really stutter or struggle but I did hear it start to die about 0.5 seconds before it actually cut out).

Some other points below

- Falls off at bang on 4000rpm every time
- Doesn't missfire
- Sometimes has a semi rough idle (doesn't hunt, just shakes the car a bit more than usual). A mechanic has checked for vacuum leaks and reckons there are none but I should probably do a smoke check

If it was just the power above 4000rpm problem then I'd be looking at fuel but the no start is a weird one, just wondering if anyone has had a similar thing.

Stewart

I seem to recall 4000rpm is the point that the varioram should actuate (assuming your C4 is a later model with it). I suspect without it working the power delivery will be compromised. I'm sure someone will be able to explain how to check its operation.

maaattholmes

I'm not sure when exactly Varioram (yes, mine does have it, should have clarified that sorry) kicks in but figured it would be around that range. I did originally think it seemed like that kind of problem but then it doesn't really explain the no start.

Unless I have 2 separate issues, maybe

95_993

First thought was Varioran, my second thought is fuel pump given starting issues.

CarreraX

I had something very similar many years ago with a 95 993 I bought used. It wouldnt pull over about 4k. I replaced everything and it turned out to be a clogged cat. The car was just always driven slowly and never really driven hard and the cat was just really clogged and it couldnt get the exhaust out. Put a used cat on it and it was fine. You can check at the 02 sensors before and after the cat and look for the difference.

pp000830

Hi Maaattholmes,
I would first, test the Varioram actuators, known failure items. Varioram-equipped cars can be identified by the bright metal intake manifold on the top of the engine with two black plastic vacuumed actuators on top of it, and one underneath it.
The upside of replacing them is that the replacement ones now use an upgraded clear silicone rubber diaphragm so when replaced most likely they will never need to be visited again.
Testing them is an easy driveway procedure to do that is described halfway down this page:
https://993servicerepair.blogspot.co...r-robbing.html
Andy

71-3.0-911

Wasn't the C4 a 1995 pre-Varioram car? Varioram triggers at 5k, not 4K. I think this is a red herring.

Any engine codes? Rough idle can trigger them. Everything together, I'd be looking at your ignition and fuel system. The rough start when warm has been attributed to a few things that may be related.

pp000830

Idle issues, back to basics:
Is the idle valve clean and working?
Is the system voltage when running above 13.5 volts?
Have you tested the distributor belt to see if it is broken?
Can you test to see if both ignition coils are producing spark?
Andy

pp000830

Hi CarreraX,
I think you are on to something.
I think your test would work on OBD-II cars with before and after CAT oxygen sensors. I would think a badly clogged CAT on these cars would also throw a CEL.
An OBD-I car with a single CAT might not.
Andy

Bill Verburg

vram hass 3 operating regimes w/ >50% throttle

<5160 long tubes, w/ closed flap
5160 5920 short tubes w/ closed flap
>5920 short tubes, w/ open flap

The tubes and flap are vacuum operated, this system is very prone to vacuum leaks

the tubes are operated by solenoids /vac on the left and d right top of the manifold, the resonance flap and actuator are under the front center of the manifold




tubes top left and right, resonance flap front under



resonance flap