zbowen

1990 F150 XLT Lariat 4.9L idles for 15 Seconds dies starts again and good to go.

When it initially starts cold as in not started and ran for the past three hours or so the truck will start fine, idles a little higher than normal but smooth all around, once it kicks down to a lower idle after initial start up it dies like it is chugging rich.

New plugs, ignition wires (both needed, plugs were older than dirt, center diodes chipped and gunked, and the lowest ohm read out on a spark plug wire was 5.5K the new ones were sub 550) new Idle Air Control valve.

This has not remedied the situation.

My next plan of attack is fuel injector cleaning/check, coolant temp sensor change and O2 sensor change. Any specific recommendations from anyone who may have dealt with this in the past? Problem persists when started in either tank (dual tanks) Once its good and going I can switch tanks flawlessly and start on either tank fine. No dummy lights when it dies after initial start. Thanks in advance.

DarrinT04

i would start by putting fuel injector cleaner in one or both of the tanks

Steve83

Don't throw part$ at it. If you still have the previous IAC, you should put it back since it wasn't the problem, and it's probably higher-quality than the replacement. What happens if you hold the RPMs up before you expect it to stall? Does it stall anyway? Or can you keep it running? If you suspect a problem with the ECT, test it. It's easy. Click these & read the captions:


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Get a Haynes, and try to follow the appropriate diagnostic procedure in Ch.5 (usually Sec.5 or 7):


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The oxygen sensor is NOT a maintenance part - it never needs to be changed, unless it's damaged. Get a fuel pressure gauge as this caption explains:


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If you really feel the need to change some parts, these actually NEED to be changed - they're known problems:


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Also check for these:


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zbowen

You can hold it with the gas pedal, it will not cause it to stall. And I know its not good to just throw parts at it but its been sitting for 15+ years. My mindset is to eventually replace all the sensors little by little any way. Thanks for the response.

Steve83

Then replace them all at once with a new truck - that would make a lot more sense.

zbowen

dont need those payments

Steve83

So why blow money on parts that are working? If it's NOT on the maintenance schedule, and there's no apparent problem with it, leave it alone.