Rough Running/Erratic Idle when Warm, LH or Vacuum?! - *VIDEO ON PAGE 5*
 

Rough Running Issue

Hey guys, going into work this morning I noticed the car was running rough. I stopped to get some coffee this morning; when I tried to restart the car it wouldn't fire on the first try. The second try it started right up, but was idling high at 1,000 RPM. It was running rough though. Putting the transmission into drive dropped the RPMs down to 600 and it started to run like crap after that. When accelerating to merge onto the freeway this morning, it felt like I had no power or throttle response, so I pulled over again.

The car was idling at 650-750, but rough still. I did an acceleration again and it felt like it wasn't down on power that time. However, when I was at speed (around 55 mph) on the freeway, I pressed the gas to speed up and it felt like the car was hesitant or lagging. I had to downshift it into 3rd in order to get some power out of it. I'm at work right now and can't really look into it, but somehow I am suspecting the MAF may be the culprit to my rough running issue this whole time. It was intermittent before, now it's constant. Everything else is new, but the MAF. It was supposedly a rebuilt unit I put on at 114,000 miles and now I have 154,000. By the way the car is running on all 8 cylinders still. LOL

Any opinions as to where to start diagnosing would be great. Thanks.

MAF should be a leading suspect. Vacuum leak, too.

If it was an '89+ I would suspect the ignition monitoring relay first.

Good luck!

Car is an '87. All vacuum lines have been replaced too.

Forgot to mention the slight gas smell when this happens....

SOOO..... Anyone wanna swap MAFs with me for about 2 hours to see how it runs? :D

Andy,

Sounds like it could be a MAF issue, if it is over-estimating airflow then the LH would squirt too much fuel and it would run rich-- poor idle and stinky. That's not a typical MAF issue-- they tend age lean, i.e. under-estimate airflow as they age. But it does happen, we had that issue with our GT which caused similar symptoms.

(In our case, the rough idle straightened itself out once the engine warmed up and the LH went closed-loop, is that happening for you also?)

Also check the engine-harness ground. The MAF and the LH are both grounded at MP-IX, upper right-rear of crankcase according to WSM. A high-resistance grund connection there could cause a bogus MAF reading by the LH. Also check the main engine ground-strap under the car on the pass side.

If you can't borrow a MAF locally check with Louie, he may be able to supply a JDS-rebuilt on a buy-it-or-return-it basis.

Cheers,

I put a PM into Louie. It would be lovely to get 928 gas mileage again rather than Ford Excursion MPGs.

By the way Jim, my car is doing the exact same thing you said about a smooth idle once it goes closed loop. You can tell it's not running right when the transmission downshifts itself as you come to a stop at a traffic light.

I tried to clean it just for sh*ts and giggles with MAF cleaner and it made it worse. I guess spraying crud off of the wires left only clean bad wiring to measure the airflow very inaccurately. :(

Hi guys, I put Louie's MAF in and it cured most of my problems. Idle is very smooth, but for some reason it is still very low. It idles aroun 400-600 RPM at times at a stoplight. I also get a small surge that bogs the car down to a stall, but the ISV catches it and returns the idle to around 600.

I checked all the vacuum lines and there aren't any loose (I did find a cracked one that I replaced, but still didnt' cure the problem).

The only other thing I can think of is a fuel delivery issue causing the surge. Everything has been replaced with the injectors and the fuel pressure regulator (not the diaphragm dampeners since those hold vacuum still and probably aren't the cause). I think the fuel filter may need to be changed too since I don't remember the last time I changed it.

Any other thoughts would be welcome. Right now, it's a night and day improvement with a new MAF and my car isn't getting like 13 mpgs anymore. :)

Age of ISV?
Lube ISV with some spray lube to see if that helps.

ISV?

It's brand new. Can it still stick though?

are the hoses that connect the ISV new there have been cases of the longer curved one splitting near the clamp

They are. In fact one of them had to be returned because it was defective (cracked already) when I bought the hoses to do my intake service.


I'm pretty much ready to say screw it and try and live with it. However it is rather embarrassing to have your car stall/bog at a light. :banghead: