1994 Plymouth Acclaim Extremely rough idle, won't rev

I’m working on my brother’s Acclaim that recently started running very poorly. At idle, the engine shakes violently and nearly stalls. If you try to rev the engine, it runs even poorer and with the air filter and housing removed raw fuel drops are visible coming up from the throttle body. There is a noticeable fuel smell. The check engine light is on and it is reporting a 13, MAP vacuum error. There are no apparent vacuum leaks. I replaced the MAP sensor with no success. Oddly enough, if I introduce a vacuum leak into the system by removing the hose going to the brake booster the engine runs much better. This tells me that there is not enough air going through the throttle body to burn all the fuel. Am I looking at rebuilding the throttle body or is there another potential issue? I don’t want to spend a lot of money on the car since it will probably be replaced by the end of the year, but I need to get it running until then.

Thanks in advance.

Removing the vacuum hose introduces more air into the engine to compensate for the excess fuel that’s entering the engine. So it’s not a problem with not enough air entering the engine, but instead there’s too much fuel entering the engine.

The first thing to check for this problem is a leaking fuel pressure regulator. If the diaphram in the fuel pressure regulator has developed a leak, excess fuel can be drawn into the engine via the regulator vacuum hose. Locate the regulator on the fuel rail. It’s a small metal canister located on the fuel rail with a single vacuum hose attached. Remove the vacuum hose from the regulator, and if fuel leaks out of this connection, the regulator diaphram has a leak and the regulator requires replacement. If you find this is the problem, you should also consider changing the oil and filter after the repair. If regulator leak is severe enough, raw fuel can contaminate the oil.


If you have the 4 cylinder engine, the fuel pressure regulator is part of the fuel injector. I would replace the regulator/injector and see what happens.

Check the vacuum hose to the map sensor. Make sure there are no leaks. Chrysler used hard plastic tubing for some of the vacuum lines elsewhere on the engine. They become brittle and break like uncooked spagetti, so check everything carefully. On my 93 sundance, I got rid of all the hard plastic lines and replaced them with hoses.

One problem I have seen on Chrysler 2.5Ls is a hidden break in the line going to the MAP sensor giving the vacuum error. Put a vacuum gauge on the hose to the MAP sensor and see if you actually have manifold vacuum. Without manifold pressure data the engine will run very poorly.

Hope that helps.

I had to replace all the vacuum hoses and connections on our '91 acclaim as they were breaking just by touching them. Hoses had hardened up and become brittle. It ran much better after that… for about a year.

A nice car, ruined many by cheap minor parts. It’s the car that ended my love affair with american products