As I was driving my 1990 Allante today, it seemed to have less and less power, and the gas mileage - according to the display - was only averaging about 6mpg.
The loss of power kept getting worse and worse. By the time I got home, I could barely make it up little hills in my subdivision, whereas I'd usually fly right through with no trouble whatsoever. The "check engine soon" light came on, and I checked the codes and it returned E030.
Thought it may be a clogged fuel filter, but when I loosened the engine-side nut on the filter, plenty of gas began to flow out, so I tightened it back up and didn't change it.
Earlier in the day, the car had been on a dynamometer for a state emissions inspection, and passed. It began really losing power during the next 15 or 20 miles of driving after that.
After letting the car sit for 24 hours, I started it again and about 95% of normal engine power had returned.
I drove it 5 miles at speeds up 55 mph over somewhat hilly terrain and it ran pretty normally, although it didn't have blazing, super-responsive power. But don't forget: before, it didn't even have enough power to back out the driveway.
After 5 miles, it had a little more trouble getting up a hill near my house than it should have, so I decided to go home and put it away rather than driving it farther.
So, possibly the problem has to do with something that is OK when the car is cool, but gets progressively worse as the car and parts heat up.
That lends more credence to the cat converter restricted issue. Sometimes the converter will rattle when hit with a rubber mallet confirming broken strata within. They say with a vacuum gauge hooked up to a constant vacuum souce like one at the throttle body, then the engine revved up quickly, the reading should never fall to zero if the exhaust is not restricted. I've never confirmed this myself. Any good muffler shop can verify for free.
Thanks for the tip on how to check for a restricted exhaust.
However, I was making no progress so I brought the car into the shop where they diagnosed the problem as being four bad fuel injectors. Cost a thousand dollars to fix, but at the moment it's running really great.
