2005 Grand Caravan with just under 50,000 miles. Automatic transmission. 3.3 Liter Engine.

Over the past year, every once in a while at low speeds when the tranny is ready to change gears and I slow down instead of either speeding up or keeping the same speed, the tranny would downshift hard. An example would be in a parking lot when you slow down for a speed bump, or stuck in traffic and constantly speeding up and slowing down but never having a chance to really speed up. This has not worried me much because normal and even extreme driving conditions (e.g. climbing mountains) has been just fine, in fact quite smooth.

Now that summer is here and the A/C runs full blast (we live in Phoenix, AZ), I have noticed a few other symptoms:

[1] One day when I was backing up it felt like the van was missing or the tranny was slipping. the strange thing was if I let off the brake completely it would clear up. It would only happen if I had some pressure on the brake pedal but was still backing up. (This has only happened once.) It seems like when I first start driving and if I accelerate slowly I can almost feel the same symptom but it either clears up quickly or I am imaging it. If I accelerate quickly it does not happen.

[2] When you come to a stop, after you have been at a stop for a few seconds the van will "surge". It only happens once so I am not sure if it is a surge, or a miss, or something else. Sometimes it will happen a second time. It almost seems like it stops when I press on the brake pedal a little harder, but it is possible that it only happens once or twice per stop and I just happen to put more pressure on the pedal after it has cleared up.

Not sure if [1] and [2] are related to each other, related to the A/C, or possibly even related to the heat. I would be willing to bet they are not related to the heat because when I drive the van without the family I leave the A/C off and it runs good.

Anyone have similar symptoms? Any ideas how I can further troubleshoot the symptoms? I would love to write it off as a power shortage due to the A/C running but we drove the van all last summer with none of the symptoms. Thanks in advance.

Andy

 

One of the symptoms seems to be happening a little more often. Once we come to a stop I can feel some sort of a "clunk" that seems to come from somewhere other than the motor. Perhaps a mount or the transmission or torque converter? It does not make a difference on the RPMs. Seems to happen more when backing up, and it can (and usually does) happen more than once, especially when using reverse.

 

Could it be a vacuum leak somewhere in the brake system since it seems to rear its ugly head when the brakes are applied? I am just brainstorming here and hoping if I bring up enough suggestions someone will have run accros a similar problem and could suggest a fix or more troubleshooting ideas.

 

The van started running really bad tonight so I decided to bring it in for a scan. On my way there the check engine light came on, and the scan indicated a miss on cylinder three. The parts store only had one plug in stock so I bought that along with a set of wires and replaced the plug and wire on number three and so far it has fixed the problems/symptoms.