1990 f150 idle problems
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1990 f150 idle problems
1990 f 150 302 5.0 no a/c e40d trans /shift kit 2 wd. no smog control dual exhaust no cats. msd ignition headers. truck starts great cold runs great cold. ounce the truck gets to operating temp it will not idle in park or neutral with out throttle help. idle speed goes up and down from around 500 rpm-800 when the truck is in gear. iac is working properly and the o2 sensor is new. any ideas on what could be the problem.
Logistics Pro
Joined: Mar 2005
Posts: 4,698
Likes: 47
From: Mexico, Missouri
Have you tried to pull codes? Is the CEL on?
It definately appears that you have a problem with the truck once the ECM enters CLOSED Loop mode. A variety of ideas is the MAP sensor, ECT sensor, IAT sensor. Incorrectly set TPS, either from installation, or the TP stop screw on the TB. Have you checked Timing? If you don't have an OBDI scanner, i.e., Equus Code Reader 3145, you can check this site for an easy way to pull codes for free.
Ford Fuel Injection » How To Run a Self-Test
It definately appears that you have a problem with the truck once the ECM enters CLOSED Loop mode. A variety of ideas is the MAP sensor, ECT sensor, IAT sensor. Incorrectly set TPS, either from installation, or the TP stop screw on the TB. Have you checked Timing? If you don't have an OBDI scanner, i.e., Equus Code Reader 3145, you can check this site for an easy way to pull codes for free.
Ford Fuel Injection » How To Run a Self-Test
Logistics Pro
Joined: Mar 2005
Posts: 4,698
Likes: 47
From: Mexico, Missouri
Has the CEL been on? It's like shooting for blanks without checking for stored codes from the ECM.
Any of the mentioned parts above can give you rolling idle problem's. A rolling idle can also be an unmetered vacuum leak. Have you checked for vacuum leak's? Have you checked the PCV valve? It is a metered vac leak to the manifold for blowby gases. If it isn't a Motorcraft PCV valve, it's junk in my opinion. Even the hose that connects it to the Plenum can become cracked and cause a vacuum leak.
Any of the mentioned parts above can give you rolling idle problem's. A rolling idle can also be an unmetered vacuum leak. Have you checked for vacuum leak's? Have you checked the PCV valve? It is a metered vac leak to the manifold for blowby gases. If it isn't a Motorcraft PCV valve, it's junk in my opinion. Even the hose that connects it to the Plenum can become cracked and cause a vacuum leak.
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