I recently had a P0303 code happen while I was also noticing an undiagnosed coolant leak. There was a pool of coolant forming in theat gap under the intake manifold. And a previous visit to the shop where they did head gaskets 4 years earlier warned me that the intake gaskets were going to need replacing again soon. So the particular shop (not the one that did head gaskets) I brought it to (very reputable) is right across from where I work and the thing started acting up when leaving work so location and convenience made me take it there. They replaced the gaskets and the thing was running like new again. They also replaced plugs and wires and the thermostat while they had it apart. And they also did compression and leak tests and everything checked out well within all tolerances.

Now that brings us to today. It's one week since the repair. My wife went out to start it and guess what, it gave us a P0304 and the thing was misfiring and shaking just like it did with the original P0303. We wanted to puke. So I went back to the shop after work and they said not to worry everything is covered and they'd even pay to have it towed. When I got home I looked under the hood for anything obvious and did not find anything. Started it several times and still the steady misfire. Finally I put everything back together and and closed the hood to turn it around in the driveway for the tow truck. When I tried to start it is cranked and fired slightly but ultimately did not start. I thought great now it won't start. Tried again and it started and ran as smooth as glass. Took it for a ride and it performed great with all the power it ever had.

So now what? I'm not going to contest them replacing the gaskets because it needed it and I gave them permission to do the work. But I wonder if the original P0303 was caused by something else. Is there maybe an intermittent ignition problem? Or something else? Any ideas out there?

You need to get more data. Hopefully it will show up again and keep missing. Guessing what is wrong isn't going to help your peace of mind or pocket book at this stage.
Post the year and the miles.

It's a 1998 with 138000 miles. I took it for a ride later last night after it started running fine and eventually the SES turned off. It's been running fine today.

I recently had a P0303 code happen while I was also noticing an undiagnosed coolant leak. There was a pool of coolant forming in theat gap under the intake manifold. And a previous visit to the shop where they did head gaskets 4 years earlier warned me that the intake gaskets were going to need replacing again soon. So the particular shop (not the one that did head gaskets) I brought it to (very reputable) is right across from where I work and the thing started acting up when leaving work so location and convenience made me take it there. They replaced the gaskets and the thing was running like new again. They also replaced plugs and wires and the thermostat while they had it apart. And they also did compression and leak tests and everything checked out well within all tolerances.

Now that brings us to today. It's one week since the repair. My wife went out to start it and guess what, it gave us a P0304 and the thing was misfiring and shaking just like it did with the original P0303. We wanted to puke. So I went back to the shop after work and they said not to worry everything is covered and they'd even pay to have it towed. When I got home I looked under the hood for anything obvious and did not find anything. Started it several times and still the steady misfire. Finally I put everything back together and and closed the hood to turn it around in the driveway for the tow truck. When I tried to start it is cranked and fired slightly but ultimately did not start. I thought great now it won't start. Tried again and it started and ran as smooth as glass. Took it for a ride and it performed great with all the power it ever had.

So now what? I'm not going to contest them replacing the gaskets because it needed it and I gave them permission to do the work. But I wonder if the original P0303 was caused by something else. Is there maybe an intermittent ignition problem? Or something else? Any ideas out there?

So it's at the shop... Right?

No it's not at the shop. Today and tomorrow will not work well for losing it to the shop. It is running fine. We will be bringing it in Thursday. They will not charge us for the checkup (unless they find something else wrong with it). They are good people and just want to look over the work they did and then some.

Followup. I took it to the shop, they did an inspection and found everything to be ok. And it has been working fine now since. But every drive in it I worry about when it will blow up next. We plan to keep it for a while simply because we just poured more money into it. But we will not do a repair like this again. Next time it happens, and I own it, it's junk.

The Venture is running great and have had no problems since the repair. But,,, there's always a but. I was just checking things out and noticed the coolant color was kinda brownish. Or more of a deeper and cloudy red. And smells different. Not sure how to describe the smell but not the normal sweet smell. It is not losing any coolant. And when hot the coolant in the tank does not go noticeably higher. The oil looks perfectly clean and right at the full level all the time. No unusual smoke at the exhaust. I find no symptoms to indicate something is wrong except for the coolant color. When I took it back to the garage (weeks ago) that did the service I told them to test the coolant because I noticed the color then. They said it tested clear of oil and exhaust. I would think they would have filled the thing with fresh coolant when they did the intake gaskets. But I was pretty hard on them and their pricing because I didn't want to spend any more money on the repair than I had to. I wonder if they reused the old coolant to save some money. Anyone have any suggestions? I plan to replace the coolant and see if the new stuff stays clean. One more thing. Can you buy the coolant testing stuff at the local parts store?

Another update. Looking for some advice. The van has been running great since my last reply. But today when leaving a store it started misfiring again. Same exact shaking engine and eventually the SES light comes on and starts flashing. P0304, same as last time. Because the thing recovered on its own before I thought I'd take the chance and drive it. The store is only a mile from home. At about 3/4 of a mile into it the light stopped flashing and it was running smooth again. So that the $#@&??? Does anyone have any suggestions? Could coil packs have intermittent problems like this that would fix themselves? Please read my original post to understand what lead me to creating this thread.

P.S. I have no coolant leaks, I'm not loosing coolant through combustion and the oil is clean of coolant so I hope the problem is not with any gaskets.

dj,
Have you had the ignition system thoroughly checked out?

Coils tested? I don't think coil packs correct themselves, no.

Pugs and plug wires replaced?

You MAY have a bad ground connection somewhere.

How are you getting the SES codes? A decent scanner should also provide you with the freeze frame data that stored when the code set. It might help determine where to look.

I'm reading the codes with my scanner. But it mustn't be a (decent) one because it does not supply freeze frame data. For the benefit of everyone reading this (and me) just what will the freeze frame data do for me?

I purchased the scanner a few years ago when 3 different repair shops failed to successfully diagnose a problem with my Saturn. I was new to the game of OBDII and was looking for a good deal on an entry level scanner. I really didn't pay much attention to the higher end models. After receiving my $70 scanner in the mail from Amazon.com it took me about 15 minutes to find the problem.