starts fine, smooth idle 30secs, rough idle, then dies

It may not be running long enough to even set a code. May be safe to assume, as the OP has not commented on seeing a check engine light. The early ECMs were not all that smart in concluding what is wrong. They were barely fast enough to make the engine run. The next generation was tons better.

Hooking up a laptop can be done by purchasing an adapter cable and some try-before-you-buy software. You can verify sensors and commands. It would at least tell you what it is not, but you will still have to figure out what is broken. I would still use the techniques already given, as a stuck injector or a bad coil will not show up on the ECM. The ECMs are not that smart. You may see the injector pulsewidth slam wide open, but that could happen anyway as the ECM is just trying its best to keep the engine running. Don't let the ECM add confusion. Its still an engine with all the same mechanical parts of the old days. If it's not the fuel, its the spark, if it's not the spark, its the fuel.

Bikeboy57 wrote:
Hi April,

Lets do some things to narrow down the search. First, you said it is a tbi engine. Cool, that means that there is a computer, primitive by today's standards, that controls the engine. Lets see if we can cut the problem in half, whether it is fuel or electronic.

If I read your posts correctly, it cranks, runs 30 seconds and dies. Every time? Is that behavior consistent? The answer is important.

When the engine dies, does it die suddenly or does it sputter and die?

All computer controlled car engines start in a fuel enriched mode for the first seconds, and then convert to a preprogammed fuel map. It sounds to me like that when your engine computer is converting from the fuel enriched start to the fuel map that the engine dies. The fuel map in a late 80s GM would be based on engine temp, air temp, and rpm. If the computer doesn't detect one of those sensors, or the rpm sensor, it will shut the engine down because it doesn't know what to do. First order of business is to find all those sensors and simply unplug them, squirt contact cleaner on the connections, and plug them back in. Even better would be to have the codes read on the computer while the engine misbehaves. Even those era computers will interface with a code reader.

So that's the electrical side. If the engine cranks fine, dies suddenly everytime at thirty seconds, I am not suspecting fuel problems. Will the engine rev up during that thirty second? If it dies when you rev it, then it may be fuel. Two other posters have suggested to spray starting fluid into the intake to see if you can force it to run. If it dies when you are doing this any way, then you have eliminated fuel as the culprit.

Try to get the codes read, the hundred bucks you will spend for a code reader will pay for itself by the time you replace the second "guess at it' part.

The older OBD can usually be read with a paperclip and the internet to decipher what the blinks on the CEL mean. Look it up: might save you a few bucks on a "Code Scanner"

Hi April,

Lets do some things to narrow down the search. First, you said it is a tbi engine. Cool, that means that there is a computer, primitive by today's standards, that controls the engine. Lets see if we can cut the problem in half, whether it is fuel or electronic.

If I read your posts correctly, it cranks, runs 30 seconds and dies. Every time? Is that behavior consistent? The answer is important.

When the engine dies, does it die suddenly or does it sputter and die?

All computer controlled car engines start in a fuel enriched mode for the first seconds, and then convert to a preprogammed fuel map. It sounds to me like that when your engine computer is converting from the fuel enriched start to the fuel map that the engine dies. The fuel map in a late 80s GM would be based on engine temp, air temp, and rpm. If the computer doesn't detect one of those sensors, or the rpm sensor, it will shut the engine down because it doesn't know what to do. First order of business is to find all those sensors and simply unplug them, squirt contact cleaner on the connections, and plug them back in. Even better would be to have the codes read on the computer while the engine misbehaves. Even those era computers will interface with a code reader.

So that's the electrical side. If the engine cranks fine, dies suddenly everytime at thirty seconds, I am not suspecting fuel problems. Will the engine rev up during that thirty second? If it dies when you rev it, then it may be fuel. Two other posters have suggested to spray starting fluid into the intake to see if you can force it to run. If it dies when you are doing this any way, then you have eliminated fuel as the culprit.

Try to get the codes read, the hundred bucks you will spend for a code reader will pay for itself by the time you replace the second "guess at it' part.

The white vapor keeps sticking in my mind. Have you checked the radiator fluid? Is there a leak in the intake manifold gasket causing fluid to be sucked into the intake?

My 82 PA 454 4 bbl just had the same problem it was just a spudering and coughing,and lots of black smoke out the tail pipes enough to cover the grass in the yard. If I held open the butterfly it would work it self out of it. Turns out it was the choke pull off. Replaced it @ $35.00 bucks and now she is starting and running just like the summer time. I would try starting it with the air cleaner cover off and watch and see if the butterfly starts to open at all or try and open it with your fingers and see if she starts running better. By the way she (ours) has 2 fuel filters under the passenger side of the MH and then there is one @ the carb. JMO hope this helps, maybe, let us know.
Good Luck, Tim
Opp's is this a fuel injected motor? is so sorry

Back to basics. As stated earlier by another poster, as it gets ready to die spray a little starting fluid in the throttle body. If it picks back up you know you aren't getting fuel. Some early P30's had two fuel pumps even with TBI, one mechanical on the motor just like the earlier Quadrajets, and a electronic pump in the rear but not in the tank like most fuel injected motors. If it has this setup, the back pump may not be working correctly.

I've had these symptoms several times with fuel injected vehicles. If it is TBI fuel injection, the TBI unit needs to be removed and cleaned. Clean the idle air circuit and the butterfly, they are probably gunk'd up. Use throttle body cleaner and lots of rags. Remove the IAC valve and clean the pintle. Probably plenty of youtube videos to watch if unfamiliar. Install throttle body with new gasket. While it is apart, clean the mass airflow sensor MAF (if equipped) with spray electronic cleaner, both cleaners available at most auto parts stores.

april10 wrote:
We have a 1990 Southwind motorhome. Ran fine until recently. Now, it starts right up, runs good for about 30 sec., then the idle gets rough, the motor sounds like it's surging, and it dies. My husband cleaned out the fuel filter (there's only one) but its not the problem. Any suggestions would be greatly appreciated! Thanks!.

With a 1990 and most likely an 88 or 89 chassis, are we still talking carburetor here and if so, how about a stuck choke, considering the cold/hot symptoms. Does it have a heat riser and if so, they are notorious for sticking shut. Whatever the case, it sounds like it's running way to rich for a warm engine. You might take a look inside the tail pipe for black soot and another tell tell sign.

Yes but if the oil pressure switch is not doing it's job.. ...

Had it happen once where after an oil change my car would not start properly.. Turns out the technician had knocked the connector off the sensor while changing the oil filter next to it.

Since this is page 2 I won't belabor but.. I have to agree it sounds like a fuel issue. This switch, Filter, or other obstruction between tank and delivery system.. IF it's carborated, the float valve.

Oh.. True story..

Had a Honda EU-2000i that would only run a few minutes and die.. Three "Experts" tried to fix it, No joy.. Finally I ask if they opened the fuel vent valve to let air into the fuel tank......

WOrked fine after that.

I do not own a EU-2000i, never worked on one, Do not think I even touched this one,, But I read the forums a lot and guess what.... I recalled a "Hint" from some of the messages here.. Worked too.

sjholt wrote:
I think the problem is in the fuel pump relay system.
When you first turn it on the pump pressurizes and then when the main relay is suppose to run the pump it doesn't.
Check you fuel pump relays.

Nope! The fuel pump runs with the oil pressure switch. The relay is only used when starting, when oil pressure builds it closes the oil pressure switch and runs until the ignition switch is turned off or you lose oil pressure.