Running Rough

jlb · Mar 6, 2012

Hello everyone first of all I would like to say how great this site is and how helpful it is,ok and now to my problem for months now my 90 bronco 351 EFI has had me stumped when i go and start it in the cold it idles around 2200 rpms and runs really rough until the temp hits around 190 to 200 if I try and take off before then it will stall and I will have to wait a few before it will start back up and even while driving after normal operating temperature it tends to run rough while sitting at a light the idle will tend to lope once in a while this problem is really becoming a headache any help would be greatly appreciated thanks.

Krafty · Mar 6, 2012

when was the last time you did a tune up/ checked the plugs?

miesk5 · Mar 6, 2012

yo jlb,

Do a Self Test for Diagnostic Trouble Codes (DTC)s by my pal, BroncoJoe19

http://broncozone.com/topic/14269-code-reader/page__pid__74587__mode__threaded

The engine temperature must be greater than 50° F for the Key On Engine Off (KOEO) Self-Test and greater than 180° F for the Key On Engine Running (KOER) Self-Test.

Run it around to heat the engine up and shift thru all gears incl Reverse. Then turn off all accessories/lights, etc.

Make sure A/C is off and transmission is in Park (automatic) or in Neutral for a Manual & release clutch.

Do Key On Engine Off (KOEO) portion first.

Look Codes up in my broncolinks.com site using the new Search function.

And Post em here according to:

KOEO

&

KOER

jlb · Mar 6, 2012

Krafty said:
when was the last time you did a tune up/ checked the plugs?

jlb · Mar 6, 2012

I tuned it up about a month ago

Rons beast · Mar 6, 2012

What you describe are symptoms of an engine running too lean. Do the checks as Miesk5 suggested. Also check for cracked or broken vacuum lines. The EGR valve may be sticking open or getting vacuum when the engine is too cold. Disconnect and check for vacuum at the EGR. There should not be any vacuum when the engine is clear cold, even at fast idle. If so you need to search down the reason there is a vacuum signal. A bad temp sensor, or vacuum switch could cause this.

The EGR could be stuck...tap the top with a small ballpeen hammer or screwdriver handle, and see if the idle smooths out. If so the EGR needs replaced.

When the eng is warmed up and idling, spray some carb cleaner around the base of the manifold and by the pcv valve and other vacuum lines. An increase of rpm indicates a leak.

Do you checks dillegently, and post here what you find.

Good Luck

jlb · Mar 6, 2012

Rons beast said:
What you describe are symptoms of an engine running too lean. Do the checks as Miesk5 suggested. Also check for cracked or broken vacuum lines. The EGR valve may be sticking open or getting vacuum when the engine is too cold. Disconnect and check for vacuum at the EGR. There should not be any vacuum when the engine is clear cold, even at fast idle. If so you need to search down the reason there is a vacuum signal. A bad temp sensor, or vacuum switch could cause this.

The EGR could be stuck...tap the top with a small ballpeen hammer or screwdriver handle, and see if the idle smooths out. If so the EGR needs replaced.

When the eng is warmed up and idling, spray some carb cleaner around the base of the manifold and by the pcv valve and other vacuum lines. An increase of rpm indicates a leak.

Do you checks dillegently, and post here what you find.

Good Luck

jlb · Mar 6, 2012

I replaced the egr valve and and temp sensor and the pcv valve about a month ago when I did the tune up but haven't checked the vacuum lines.I also recently replaced the temp gauge is there a way to check and see if its sucking air.thanks for all the info will post what I found

Rons beast · Mar 6, 2012

Hey Jlb,

Do all the checks as described, remember or better yet record the results.

The temp guage is not the same thing as a temp. sensor, and there may be more than one on the engine.

With the engine warm and running spray carb cleaner, around the base of the manifold, and around any vacuum lines. Wear eye protection so the engine fan doesn't blow it into your eyes. If the engine spped increases, or the idle smooths out, there is a vacuum leak where you sprayed the cleaner. Then you have to turn the engine off and get in there and look for broken lines, cracks, lines off, etc. There could be a vacuum leak in the brake booster! clamp the line shut or plug it at the booster.

There is no "magic" to finding the source of these kinds of problems. You have to be dilligent and regimented, and patient.

Do the checks. Eliminate items. Move on the the next one. Be systematic.

Do the KOEO and KOER ...FIRST... as Miesk5 suggested, look up the codes and post them here.

We'll go from there.

Running Rough

jlb

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Krafty

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miesk5

96 Bronco 5.0

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Rons beast

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