Jerky low speeds 3.2 carrera

[cafe_racer]

Hi All,

I have a fairly stock 3.2 Carrera with a Wong chip and M&K exhaust, when slowly creeping forward in 1st or 2nd gear the car can be quite jerky sometimes. The only way to stop this is to put foot on the clutch and coast.

It's those scenarios where I am wanting to go 5-10kph and creep forward. Is this a symptom of bad driving or perhaps something mechanical?

[adias]

Stall speed on these engines is quite high, so yes, as you slow to a stop you have to engage the clutch early.

[Sajan]

I noticed the same thing. I think it's just a "that's how it works" situation.

[caitov]

Originally Posted by Sajan

I noticed the same thing. I think it's just a "that's how it works" situation.

Yep. It's normal. You just get the feel for when you need to depress the clutch.

[Snitzler]

1988 3.2, the same. It doesn't like low revs in 1st or 2nd gear. That's why I don't like driving in heavy traffic. I always thought that the engine was loading up and I would rev to clear but it didn't make any difference.

[wildthing]

How low do you guys let it go? I’ve rarely experienced this, but maybe because I cut my teeth driving a Beetle...

[Bill Douglas]

Yep.

They aren't very good town cars. First gear is very high and they don't like low rev's. Especially laboring at low rev's.

My SC tend to be "We're off, stop, we're off, stop..." etc. Hard work in walking pace traffic.

[cafe_racer]

Thanks all, good to know it's not just me! I had an SC prior which felt a bit better at low speeds in traffic so thought something might be up.

[FrankM_]

OK, and I was about to open up my AFM to try to fix this 'problem', but apparently it is normal behaviour. Very annoying anything lower than 25 km/h (15 mph) is an issue on mine (85 Carrera)

[Peter M]

They have a fuel cut out when the engine is above 1300rpm and the throttle is closed that may contribute to the jerkiness. I also recall posts suggesting wear on the resistor track of the AFM makes them worse.

EDIT: Found one:
[3.2 Motronic] Air Flow Meter wiper arm re-tracked - WOW!

PS. My 3.2's have never liked low speed running either

[jlex]

My '85 was pretty bad, but installing a Steve Wong chip helped it considerably. The '88 isn't quite as bad, but it's there. No chip yet so I can't say if it'll improve.

[Missed Approach]

Hi cafe_racer- I did notice a sizeable improvement in low-speed operation once I retracked the AFM. Here's my story...

Air Flow Meter Adjustment!

[AG81]

Originally Posted by caitov

yep. It's normal. You just get the feel for when you need to depress the clutch.

^
x2

[Quicksilver]

My 87 had issues with jerking and surging at low RPMs until I went through it and replaced the intake gaskets, intake spacers, a whole bunch of dried and hardened old rubber, and had the DME's solder joints reflowed.
Since then the car will smoothly crawl along at idle.

[jlex]

Originally Posted by Quicksilver

My 87 had issues with jerking and surging at low RPMs until I went through it and replaced the intake gaskets, intake spacers, a whole bunch of dried and hardened old rubber, and had the DME's solder joints reflowed.
Since then the car will smoothly crawl along at idle.

So you're thinking it's more like vacuum leaks (lower rpm's, less vacuum). Would be nice to have driven a brand new one off the showroom floor to see if they had that problem. I guess if someone has just overhauled an engine, they could confirm if the problem still persists...

[pmax]

Originally Posted by cafe_racer

Hi All,

I have a fairly stock 3.2 Carrera with a Wong chip and M&K exhaust, when slowly creeping forward in 1st or 2nd gear the car can be quite jerky sometimes.

That's not normal. My 87 runs smooth at parking lot speeds.

I agree with the others yours might have a vacuum leak.

[NutmegCarrera]

I would not agree that this is normal. I had similar issues when I got my ‘85. Through all of the research, etc... I learned about the “Barndoor” AFM. The contact wiper wears a path in the mating piece (the air flow is measured by how far the “bar door” opens, and that position is reflected through a variable resistance (?) strip. Much like old R/C car speed controllers). By changing where the contact arm “wipes” this surface - you can smooth things out considerably.
I’m sure there are better words to describe the components I describe - but this is the experience that I had. I did find a procedure for opening and adjusting this somewhere. May have been in the 944 forum. The Motronic system uses this type of air flow measurement.
Not discounting vacuum leaks, bad sensors, and the like.

Don’t accept a car that bucks and stutters. These things should be smooth.

Good luck.

[Hnichols]

Does the jerkiness occur even after the motor is warmed up? In my experience, the jerkiness -- actually a pretty violent bucking -- caused by worn track in the AFM was basically a cold engine phenomenon.

I agree that your should run smoothly at low rpms.

[Quicksilver]

Originally Posted by jlex

So you're thinking it's more like vacuum leaks (lower rpm's, less vacuum). Would be nice to have driven a brand new one off the showroom floor to see if they had that problem. I guess if someone has just overhauled an engine, they could confirm if the problem still persists...

I call that whole episode "The Rubber Explosion Incident™". I found cracks in some of the hoses on the front side of the engine and the big breather hose was so hard I assumed it was made from some sort of plastic. (I was shocked to find out how soft the new hose was!) I also discovered that the crimps on the fuel lines to the injector lines were so degraded that the fittings were spinning like they were bearings. (They hadn't leaked a drop either.)
I knew the intake gaskets were leaking but when I pulled the manifold off I was surprised to find that the plastic manifold spacers had eroded too.

Fixing all of the above really smoothed it out but I also had the DME reflowed and while I was in there I replaced the 24-pin chip with the last factory 28-pin chip. That made it idle better then it had when I bought it at 110K miles back in 99. The DME needed the reflow but the 28 pin chip upgrade raised the idle from 800 to 880 rpm which would make some difference.

I really feel that absolutely eliminating all vacuum leaks was the biggest fix. It really brought it all together.

[Sabai]

I had a similar issue before replacing the ICV and addressing a couple vacuum leaks.


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