I'm getting a restricted performance with the following codes:

P1316
P0171
P0174
P0300 and all of its friends 1-8.

The car sometimes runs rough. It was worse last week when I filled up the car and it immediately began misbehaving. Apparently it was the last of the gas they had at the station. I filled up again and added some Lucas fuel injector cleaner and fuel stabilizer and the condition became better. Both the codes and the restricted peorformance became more infrequent, but they're still present.

The symptoms are the following:

A somewhat rough idle after cold starts
Misfires under heavy acceleration, between 3 and 4k rpms. However after 4k rpm the misfires disappear and she really pulls hard.
When the restricted performance light comes on, acceleration becomes sluggish. Even after clearing it. To get back to normal acceleration, I have to stop the engine after clearing the codes.

I've also noticed a slightly deeper exhaust note.

I have no idea what to check. I'm starting to think that this can't just be bad fuel. I was thinking of checking to see if there's any water in the coils that could've gotten there after the last time I washed the car and the engine. While I'm at it, I thnk it would be a good idea to check if the coils had any oil on them and if the sparks are good.

What are the likely causes for these symptoms?

 

Read fuel trims. Probably an air leak but that's a way to find out. Or smoke test...

 

I still haven't gotten around to doing anything but I did I notice the following. The o-ring around the base of the MAFS is out of shape.

 

Post #2....

 

Thanks Michael. I don’t understand what allows the engine to run fine and then not and then back to running fine. I will try disconnecting one coil at a time to see if that tells me something. My prior owner replaced all the coils and plugs less than 1000 miles ago so I wasn’t focused on them. We haven’t put more than 250 miles on this car since I got it for my wife 2 years ago. She has been and is afraid it will strand her so uses other car😩. I get something fixed and another issue pops up. Hope to get this resolved and that this will make it reliable👍.

 

not much help I’m afraid,

it takes a leap of faith, and may be counterintuitive, but driving these cars more often (daily if possible) does make a positive contribution toward reliability.

In the meantime, best of luck with these issues.

Z

 

Washed the engine ...thats a big No No those coil covers rarely seal .

 

Pistonbroke wrote: “Washed the engine ...thats a big No No”

Have not washed the engine.
this morning I drove it about 15 miles. Ran very rough with restricted performance light on dash during start up and idle. Got a couple miles and all smooth….several more miles and restricted performance light disappeared. Stopped to top off the tank with best high test fuel in our area. Started up and rough idle returned but as soon as I pulled away at modest speed the rough engine disappeared and drive was beautiful. No rough running or return of restricted performance light. Is it possible that the entire issue was caused by bad fuel? We will see. Planning to get it back on the road no later than tomorrow. Will send report. Zray’s contention that the car needs to be driven is looking likely true for this one!?!

 

Jagvert, with all respect I am curious as to why this was tacked onto an unrelated 8 year old thread. Generally a better idea to start a new, more specific thread.

 

Not sure myself. I did start a separate thread. I guess I just messed up!

 

I was wondering, but since this is a thread I made, and never got around to giving the answer. The problem I was having with the XK8 back then was solved with a new intake pipe. The accordion section was broken, and was letting air escape. However, the MAFS was also bad, and replacing it along with the pipe solved the problem for good.