My '85 auto starts well even though it often sits for 2 weeks between runs. However, the last few times out it experiences a severe flat spot, no power, about 3-4 (maybe 5-6?) minutes after starting.
Typically drive about 0.5 to 1 mile normally, not hard on it as engine is cold, then it will not stall but basically only run a idle speed regardless of throttle position. If I play with the throttle it might have a slight pop back into the intake.
Episode lasts about 10-15 seconds and then all returns to normal. Drives great 5, 10, 40, or ?? miles afterwards. Does not repeat on warm engine restarts although it can be sluggish shortly after restarting when warm.
Seems like it has to be a temperature sensor turning off the fuel or some such thing but it is so repeatable and narrow in time frame I am having trouble putting my finger on it.

Any assistance would be appreciated.

 

Yep, Sounds like the Temp II sensor is suspect. Check the WSM for the values on the 85. You might try the link in my signature that has the section for the LH on the 87+. I would think the test values are the same, but you never know.

 

It could be the MAF is running weak, and this is noticable when engine is warming up and you are not on the O2 loop.

After you've checked out Temp 2 as Andrew suggests, set the idle CO as per the WSM. If you can't get idle CO up to 1% then the MAF is aged, unless you have a fuel pressure issue.

 

sounds exactly like my 86.5 when I bought it.

On my car there were a few vacuum leaks, and MAF sensor mounted backwards.
After correcting these issues she now starts and runs perfect.

cheers
Michel

 

Thanks guys, I will start with the temp II sensor and double check for vacuum leaks. The intake was refreshed a few years ago, including all of the vacuum lines, but time has a way of undoing these things. I am pretty sure I have the MAF sensor mounted correctly but at this point I will check it as well.

I have a fuel pressure guage to install, on the list of things to do, so I probably will do that at the same time.

Unfortunately the car and I are only in the same area on weekends and there are always other priorities to work around.

Once I have more information I will report back.

Thanks again.

Roger

 

I finally had a few minutes to check out the Temp II sensor, both cold and warm readings are in line with the specs.

The good news is that this time when I drove the car it didn't experience this problem.

The bad news is I got a timing belt warning. Had a TB warning last year and checked the tension (Kemf tool), low end of the guage, moved it up to the top of the window. Not many miles since then so my fear is that tension is relaxed, and that means digging deeped into the TB system. I replaced the belt, rebuild the tensioner, replaced the idler, bushings, and water pump when I got the car but maybe I missed something.

Anyway the flat spot issue will take a back seat to the timing belt issue. Once I get back to the flat spot I will let you know what else I find.

 

+-I would check the TPS as well, both cold and hot.


What kind of water pump did you use rebuilt or new??
I suggest a new Laso or the upgraded part with the new bearing

 

I don't know which water pump it was, other than a rebuild purchased from one of big 3 suppliers. No water leaks to indicate the pump shaft may be moving but I need to take it apart to check all of the parts of the TB system. Is there an external identification for the pump that would ID the manufacturer? I am pretty sure it was a metal impeller but beyond that??