'90 E-150 idles up and down
Guest
Posts: n/a
'90 E-150 idles up and down
Folks,
I have a 1990 Econoline 150 with a 302 engine. When it's warned up and the transmission is in Park or Neutral, the idle speed goes up and down. I don't have a tach so I can't give numbers, but it sounds like the speed climbs quickly to some point, then drops suddenly. When it drops, I can hear the thermactor air being dumped to atmosphere. Then it repeats the cycle, about every 2 seconds. If I press on the accellerator slightly, or if I put it in gear, it idles fine. The up-and-down cycling is less frequent when the air conditioner runs.
Other than this, the thing seems to run well (unless you count a little chattering when going uphill - higher octane gas helped here, but it hasn't fixed it completely).
Any hints on what could be causing this? Here are some things I've tried to check:
1) Throttle position sensor: resistance from either end to wiper seems to vary smoothly as throttle moves - doesn't seem to be open. Haven't checked TPS input to computer, though.
2) Throttle bypass valve: coil resistance looks like a dead short to ground. (It has only one wire in the connector - I assume this gets 12V applied when it needs to be opened.) What would be normal here?
Any suggestions? Well-meaning neighbors and mechanics of varying skill have suggested the TPS, the bypass valve, the EGR valve and position sensor, and the O2 sensor.
I haven't checked the codes yet, but I will.
I have a 1990 Econoline 150 with a 302 engine. When it's warned up and the transmission is in Park or Neutral, the idle speed goes up and down. I don't have a tach so I can't give numbers, but it sounds like the speed climbs quickly to some point, then drops suddenly. When it drops, I can hear the thermactor air being dumped to atmosphere. Then it repeats the cycle, about every 2 seconds. If I press on the accellerator slightly, or if I put it in gear, it idles fine. The up-and-down cycling is less frequent when the air conditioner runs.
Other than this, the thing seems to run well (unless you count a little chattering when going uphill - higher octane gas helped here, but it hasn't fixed it completely).
Any hints on what could be causing this? Here are some things I've tried to check:
1) Throttle position sensor: resistance from either end to wiper seems to vary smoothly as throttle moves - doesn't seem to be open. Haven't checked TPS input to computer, though.
2) Throttle bypass valve: coil resistance looks like a dead short to ground. (It has only one wire in the connector - I assume this gets 12V applied when it needs to be opened.) What would be normal here?
Any suggestions? Well-meaning neighbors and mechanics of varying skill have suggested the TPS, the bypass valve, the EGR valve and position sensor, and the O2 sensor.
I haven't checked the codes yet, but I will.
Guest
Posts: n/a
'90 E-150 idles up and down
mine does this too. but usually it only happens on the second startup of the day. its very odd.
i think what is happening to mine is the coil wire is a little loose. i know it's really simple but it could be causing the problem.
mine wouldnt start about a week or so ago and i thought it was the fuel pump or a relay since it was cranking. turns out my coil wire was wallowed out and was so loose it wasnt making contact with the coil. i changed that and it didnt do the weird idle thing on the second startup.
i think what is happening to mine is the coil wire is a little loose. i know it's really simple but it could be causing the problem.
mine wouldnt start about a week or so ago and i thought it was the fuel pump or a relay since it was cranking. turns out my coil wire was wallowed out and was so loose it wasnt making contact with the coil. i changed that and it didnt do the weird idle thing on the second startup.
