Why does your 1993 Jeep Grand Cherokee surge?

Answer 1

This is a common problem with older jeeps and from my experience is related to the fuel system. I've also heard that a cracked distributor cap or defective rotor can cause this problem and I'm sure it can but I havent found that to be the answer to what you're describing so I'll only address what I know and let others fill in lots of blanks that I leave behind.

My 95 GCLimited with 5.2L V8 experienced that surging as well as a big problem with holding an idle. Feeling that the problem was in the fuel system. I would recommend you do these things in order as I've listed them by what I feel is the cheapest and easiest fix on down the list to those that cost more and may be beyond the reach of casual repair folk such as myself.

I first made sure that all vacuum hoses were sound by listening for a hissing from those little hoses while the engine was running....it's usually fairly pronounced and if you touch a cracked hose and it breaks you usually can see it. The vacuum system is vital to the operation of the engine and those 1/4 inch rubber hoses become heat stressed and can easily crack but not completely break in two.

Secondly I replaced the PCV valve which is a device that is cheap and sticks in the top of the valve cover and has a larger breather/vacuum hose attached. They get stuck and can affect your fuel mileage and the smoothness of your engine

Third I tried a bottle of Throttle Body, Choke, Injector Cleaner in a full tank of gas assuming that it would perhaps clean the fuel injectors without having to have them removed and physically cleaned or replaced. My trusted brand is Lucas and its available in most parts stores.

By the way, none of the above worked to that point. So....

Lastly before spending money on electrical parts that attach to the fuel system at the throttle body I bought a can of spray throttle body cleaner. With the engine running and the round plastic part removed with the one nut from the top of the throttle body (find the air cleaner and follow the big black plastic air tube to the top of the throttle body), I sprayed this directly into the top of the throttle body. It immediately flooded the engine so I restarted, and located the throttle linkage beside the throttle body and gave it gas from there and more slowly sprayed more spray down into it. The Lucas branded spray is safe for engine parts and will not flash back flames (although you should always exercise care by wearing safety glasses and ALSO remembering that there's a fan belt etc running that you could be leaning over....loose clothing caught in a fan belt will REALLY ruin your day) To make a long story short this spray absolutely fixed the problem and the engines been running smoothly for several months now.

So the lesson learned here is that perhaps it never hurts to run a bottle of fuel system cleaner through your gas tank on regular intervals in order to help keep varnish and gum from plugging up the mechanical parts of your fuel system.

Again, I'll let someone more knowledgeable than I write about the Throttle Control Motor, the Idle Speed Motor, the Distributor and Rotor, the Fuel Filter and the myriad of other things that can go wrong. I've just addressed the simplest and cheapest of things and I've always been amazed that sometimes a good cleaning is all these things need to settle down and fly right.

Good luck.