New to Me 951, New To Me Misfire and Stumble Problems

[Ds1]

Hey all,

I just bought an '86 951 yesterday and its a fantastic car, but apparently a few days after it was offered for sale it started doing this stumble:

It will cut what seems like fuel when you very lightly accelerate. This can happen at any speed/gear. If you push in the clutch and let it back out as if you were starting in 1st gear that seems to solve the issue or at least get past the stumble point. After that the car drives great, the PO took me on a rather worrying 100mph ride after he got past the stumble area.

I had a 944 NA so I am somewhat familiar with these cars and also did my own turbo system on my Miata so I'm familiar with how they work too. I have seem many comments on this issue but nothing exactly the same - FPR, tune up, injectors, vacuum leak, DME relay, etc. I'm fine with checking all those things, but is there a best place to start before I spend 3 days diagnosing parts?

The car is extremely original and was in storage for 8 years. It was running and on the road for about a year then I just bought it. Thanks!

[mytrplseven]

Originally Posted by Ds1

Hey all,

I just bought an '86 951 yesterday and its a fantastic car, but apparently a few days after it was offered for sale it started doing this stumble:

It will cut what seems like fuel when you very lightly accelerate. This can happen at any speed/gear. If you push in the clutch and let it back out as if you were starting in 1st gear that seems to solve the issue or at least get past the stumble point. After that the car drives great, the PO took me on a rather worrying 100mph ride after he got past the stumble area.

I had a 944 NA so I am somewhat familiar with these cars and also did my own turbo system on my Miata so I'm familiar with how they work too. I have seem many comments on this issue but nothing exactly the same - FPR, tune up, injectors, vacuum leak, DME relay, etc. I'm fine with checking all those things, but is there a best place to start before I spend 3 days diagnosing parts?

The car is extremely original and was in storage for 8 years. It was running and on the road for about a year then I just bought it. Thanks!

Start with the fuel system. Get a pressure gauge and put it on the fuel rail to see if it meets the specs (see Clark's Garage). Also, ensure you've got good gas. Replace the fuel filter while you're at it. Also, the DME relay, that supplies power to the fuel pump, has been at the heart of weird engine running issues. I'd get a replacement from Pelican and avoid the URO brand. After that, if it still is unresolved, pull the plugs and injectors. Replace the plugs and send the injectors to Witch Hunter in Duval, WA for rebuild. They charge $100 and they're the best. Get a noid light (cheap) from auto parts store to make sure the injectors are getting pulsed. Look at the distributor cap and rotor for corrosion. Do you know when the belts were replaced last? This is a Big one to verify so you don't ruin the top end of the motor.

Good luck and keep us posted. I'm restoring the same car. It's a great education.

[Ds1]

Okay, sounds good. I'll start easiest with some seafoam and fuel filter and move from there. The car probably needs them anyway. Update soon!

[kdjones2000]

You should also check the TPS for proper operation.

[Ds1]

Is there a good way to test that?

[kdjones2000]

Clark's Garage Home Page