1978 Chrysler Aspen running rough

The 360 V8 still running pretty roughly. Put new two barrel, filters, plugs like a normal tuneup. Only 80,000 miles on the Cordoba chassis when come from Santa Fe. Had harsh idle since; don’t know why.

Have you done a compression check to make sure all the cylinders are working as designed?

So you replaced the carb, and that didn’t fix it? hmmm … on my 302 Ford truck from the same era , whenever I get a rough idle, when it starts one day for no apparent reason after it has run fine for months, it is usually caused by a vacuum leak. Check all the vacuum hoses, and test all the vacuum operated devices with a vacuum pump to make sure they hold vacuum to 20 inches.

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Are you running ethanol gas in that old car?



I have heard stories about non oem plugs causing problems. It could need carb adjustment, see if the choke opens all the way.

Don’t think so, just the Shell’s regular stuff.

Look on the pump.

Does it state 10-15% ethanol content?


Which virtually everywhere contains up to 10% ethanol. The car wasn’t designed to run on this stuff. The ethanol is eating away at the rubber parts in your car, including those fuel lines, pump and carb. It might not be your current problem - I like the vacuum leak idea - but it will cause problems for you down the road.



Those are all replaceable. When I re-built my carb last year I bought hose in bulk and replaced all of them for $few. The manual for my '87 Toyota pickup warns about the dangers of methanol, not ethanol.

For a short tutorial on ethanol in older cars;


In the article it sates you can replace rubber parts with ones more resistant to ethanol. I’d add - IF they exist! Likely a carb rebuild kit and possibly fuel pumps for a '78 Aspen do NOT exist. That just means carb rebuilding and fuel pump replacement will likely be a regular occurrence.

Since ethanol in fuel was not mandated until 2007 - a full 20 years after your Toyota’s manual was written - it was likely omitted because it was not yet an issue.

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Ethanol was mandated in Minnesota in 1992.


Methanol has never been mandated; I’ve never seen it used as an additive by gasoline manufacturers. I used to use it (Heet) in winter to dry my gas but switched to isopropanol (Iso-Heet) when that came out. But ethanol has been used as an additive that long.

No, it hasn’t been mandated, anywhere, anytime. MTBE was the additive used to reduce pollution until it was found to be a problem and eliminated.

Methanol was used as racing fuel (at Indianapolis - now they use ethanol - and sprint car racing) for a very long time and was, and is, readily available. Toyota must have figured someone would try some in the tank and decided to tell their owners. You may have used Heet, but it is unlikely you added a gallon to 9 gallons of gasoline.

Ethanol does attack nitrile rubber commonly used in older cars for fuel lines, fuel pump membranes and carburetor parts. The higher the percentage, the more aggressive the degradation. Your '87 truck will, at some point have problems from running modern gasoline. Stock up on fuel pumps, filters and carb rebuild kits if you plan on keeping this truck running.

Ethanol also corrodes the metal components of the fuel system.

That’s why we have gas that contains no ethanol in Minnesota.


Some areas have been using E10 since the late 1980’s as a winter fuel to reduce local pollution trapped by the inversion layer.

I suspect that the supply of fuel hose changed years ago to be compatible with common fuels.

Plug wires new? Compression tested?

Why was the carb replaced? To address this harsh idle symptom? If so , it is possible the replacement carb hasn’t yet been set up properly. It’s generally not possible to simply bolt a replacement carb on the intake and be done with it. There’s some further adjustments needed to tune the carb to the engine. Incorrect/unbalanced idle mixture adjustment, etc. And of course it’s possible the replacement carb has a problem too. Did the carb paperwork mention anything about “flow testing”? Is the harsh idle occurring on both a cold and warm engine? Worse on one vs the other? How does it perform at higher rpms during normal driving? What’s the cold and warm idle rpms?

Not in pickup trucks.
Some fleets use pure methanol. Nobel-prize-winning chemist George Olah thinks it’s the fuel of the future.

I definitely did, 12 ounces to 15 gallons.

Last year AutoZone had a rebuild kit in stock, as well as all the other stuff: I don’t need to stock up. Compression is still book; emissions are still book. It runs as well as new. I re-built the carb at 30 years. Other than a leaky accelerator pump, it looked good. I replaced all the hoses because it was cheap and I had everything apart. The old hoses look good.

? I find no sign of this in my pickup.

You have it for the same reason you have everything else: people pay for it. You also have cigarettes, lite beer, and lutefisk.

You definitely did not add 1 gallon to 9 per the statement above. Commercial gasoline is up to 10% ethanol, this is a 1.2% concentration

Not a relevant comment.