1991 Ford F-150 stuttering and rough idle

LEWISCYPHER

MEMBER
1991 FORD F-150
6 CYL
4WD
MANUAL
185,356 MILES

I was driving my truck and it started idling rough and stuttering under medium accelaration, if I put it to the floor it hesatates for a second then accelerates good. This problem didnt occur gradually but started suddenly. The check engine light is not comming on so I assume the emissions control sensors are working? Tried putting a set of plugs and wires in it today with no change.

Sunday, November 16th, 2008 AT 5:13 PM

3 Replies

JAMES W.

MECHANIC
2,394 POSTS

Check your EGR valve to see if it is hanging open a little bit. You may have to remove it phisically to see if it is closing. Next, you can do a resistance test on the throttle position sensor, TPS with an ohmeter. With 185K on the truck, it can wear a spot on the coil and creat a "weak" spot. The ECM will usually pick this up and trip the check engine light, but sometimes it won't until the condition gets worse. Hope this helps.

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Sunday, November 16th, 2008 AT 7:15 PM

LEWISCYPHER

MEMBER
5 POSTS

Ok I checked the EGR valve seemed like it was closing. Just to be sure I made a gasket that covered the port to the fuel injection manifold. There is only one port so I figured that would be ok for diagnostic purposes. There was no change. I also picked up a TPS It was only 25 bucks so I bought one and to no avail still running rough at idle and hesatating on acceleration. Any more ideas?

Thanks in advance!

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Tuesday, November 18th, 2008 AT 6:17 PM

JAMES W.

MECHANIC
2,394 POSTS

Lets check for a vacuum leak. With engine at a warm idle, take a can of regular carb cleaner and spray it along the intake where it meets the heads. Also any intake ports and lines. If you hit a leak anywhere the RPMs will pick up and the motor will smoothen out for just a bit. Let me know, Jim.

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Tuesday, November 18th, 2008 AT 11:37 PM