Surging Idle and drive when Cold!
Thread Starter
Junior Member
Joined: Aug 2012
Posts: 2
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Surging Idle and drive when Cold!
Hey everyone,
I recently bought a 1988 f150 with the 300 (EFI). I am having a couple issues that i'm hoping someone could help me with!
At first start up, the truck idles real rough and the RPM's jump back and forth between 500 and 1500. Sometimes it drops so low is stalls itself out. When the rpm's jump back and forth, I can feel the brake pedal slightly move in out (assuming the vacuum?). After about a minute or two, the idle (though still rough) slowly levels out at around 750-900 RPM.
If I try to drive the truck before it levels out, I have to give it lots of gas while disengaging the clutch or else it stalls. Once I get moving, without giving it proper "warm up time," the truck chugs, jerks, bounces, surges, and misfires. Again, after a few minutes the truck runs fine with no issues.
However, sometimes when I get to a red light, the truck will idle level (though rough) at 800 then randomly fall to 500, then surge itself up to 1000. Any ideas what all these issues could be?
I have replaced the plugs, wires, distributor cap, air filter, and EGR valve. I also replaced the fuel pressure regulator which fixed the problem for about a week. Since the problem has come back, I have cleaned the IAC valve and throttle body, and seafoamed the truck to no avail.
When I unplug the IAC valve sensor, the truck drops in idle and stalls. When I disconnect the MAP sensor, the truck starts then stalls, so I am assuming those are ok.
The truck sat some time before I bought it and only has 60k original miles.
Any ideas! Thanks!!!
I recently bought a 1988 f150 with the 300 (EFI). I am having a couple issues that i'm hoping someone could help me with!
At first start up, the truck idles real rough and the RPM's jump back and forth between 500 and 1500. Sometimes it drops so low is stalls itself out. When the rpm's jump back and forth, I can feel the brake pedal slightly move in out (assuming the vacuum?). After about a minute or two, the idle (though still rough) slowly levels out at around 750-900 RPM.
If I try to drive the truck before it levels out, I have to give it lots of gas while disengaging the clutch or else it stalls. Once I get moving, without giving it proper "warm up time," the truck chugs, jerks, bounces, surges, and misfires. Again, after a few minutes the truck runs fine with no issues.
However, sometimes when I get to a red light, the truck will idle level (though rough) at 800 then randomly fall to 500, then surge itself up to 1000. Any ideas what all these issues could be?
I have replaced the plugs, wires, distributor cap, air filter, and EGR valve. I also replaced the fuel pressure regulator which fixed the problem for about a week. Since the problem has come back, I have cleaned the IAC valve and throttle body, and seafoamed the truck to no avail.
When I unplug the IAC valve sensor, the truck drops in idle and stalls. When I disconnect the MAP sensor, the truck starts then stalls, so I am assuming those are ok.
The truck sat some time before I bought it and only has 60k original miles.
Any ideas! Thanks!!!
Thread Starter
Junior Member
Joined: Aug 2012
Posts: 2
Likes: 0
Update:
So I pulled the throttle out and cleaned it up real good. Then I replaced the TPS and disconnected the battery. Truck still has the same problem of bouncing idle at start up and if anything now the idle levels out a little higher around 1000. AND, now the Check Engine light is on. Any more ideas other than IAC?
So I pulled the throttle out and cleaned it up real good. Then I replaced the TPS and disconnected the battery. Truck still has the same problem of bouncing idle at start up and if anything now the idle levels out a little higher around 1000. AND, now the Check Engine light is on. Any more ideas other than IAC?
