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Rough Idle with Intermittent Lunging and Low Power Under Load

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Old 06-18-2017, 09:27 AM   #1
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Default Rough Idle with Intermittent Lunging and Low Power Under Load

Hi Everyone,
I have a '92 4.9L manual that just started having an inconsistent idle (900-1500RPM) and lunging under load with low power (when accelerating, shifting, or on hills). Otherwise, on flat roads with an easy throttle it seems to run okay. Should I start with testing IAC and TPS?

Also, the idle issue occurs both right after a cold start and while the engine is warm, and, surprisingly, no codes from the computer.

I've found a nice method for testing the TPS (http://troubleshootmyvehicle.com/for...test-the-tps-1), but haven't been able to find a good way to test the IAC. Any suggestions? Also, anything else that I should be looking for in terms of sources of the problem?

Thanks!
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Old 06-18-2017, 09:42 AM   #2
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When was the last tune-up ?
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Old 06-18-2017, 10:40 AM   #3
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When was the last tune-up ?
Less than 1 year (~4000 miles - she's not my daily driver) with new plugs, wires, and coil.
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Old 06-18-2017, 04:39 PM   #4
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Update: Checked TPS and it tests out okay. Also checked the internal resistance of the IAC (~10 ohms), which also seems to be okay. Also looked for carbon build-up, but none in sight. Unplugging the IAC while the warmed-up engine is running makes it idle low, nearly to the point of stalling. If memory serves, that's the correct response (right?).

Any other thoughts?
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Old 06-18-2017, 07:19 PM   #5
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Hi,
When you say "coil" do you mean the PIP sensor in the bottom of the distributor???

I would run codes....

Might just tell you something!
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Old 06-18-2017, 08:51 PM   #6
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So this is my first post here so hopefully I am in the right place.


I own a 87 f150 5.0 4-speed. Every morning when I start her up it will go to about 1800 rpm for about 30 seconds and then drop down to 800 rpm. I'm pretty sure this is normal but the problem is after it is all warmed up I will drive somewhere and then start it again it will do it all over again. It does it no matter how cold or hot it is. Seems like it's choking it self and there is nothing to tell it "hey, I'm warmed up no need for high rpm". I'm very puzzled. Also, after I get down the road for about 2 miles it will do a little "jerk" and it will drive and run so much better. Mind you that before it does the little jerk I will shift into 3rd and hear pinging noise or knocking but after the jerk I will shift into 3rd and it will haul a**. I'm very confused. These are the new parts I have on it.

TPS
EGR and sensor(took back sensor because there was no difference )
O2 sensor
Map sensor
Brake booster
Radiator
Iac
Cleaned the throttle body very well
Air filter

I ran the codes and I got 33 but I replaced the egr and there was no difference at all.

Someone please help before I go crazy please.

Also, the check engine light will come on but go away when I hit the gas just a little bit then come back on???? Anyone?.
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Old 06-19-2017, 05:58 AM   #7
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So.. not the right place... you need to start your own thread..
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Old 06-19-2017, 06:25 AM   #8
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It's ok. Not a big deal. Just a forum website so it don't really matter. Thanks tho ������
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Old 06-19-2017, 07:13 AM   #9
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Quote:
Originally Posted by seagiant View Post
Hi,
When you say "coil" do you mean the PIP sensor in the bottom of the distributor???

I would run codes....

Might just tell you something!
I was referring to the ignition coil and can there be codes if the CEL isn't on?

Thanks!
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Old 06-19-2017, 10:02 AM   #10
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Quote:
Originally Posted by Southern_tree View Post
So this is my first post here so hopefully I am in the right place.


I own a 87 f150 5.0 4-speed. Every morning when I start her up it will go to about 1800 rpm for about 30 seconds and then drop down to 800 rpm. I'm pretty sure this is normal but the problem is after it is all warmed up I will drive somewhere and then start it again it will do it all over again. It does it no matter how cold or hot it is. Seems like it's choking it self and there is nothing to tell it "hey, I'm warmed up no need for high rpm". I'm very puzzled. Also, after I get down the road for about 2 miles it will do a little "jerk" and it will drive and run so much better. Mind you that before it does the little jerk I will shift into 3rd and hear pinging noise or knocking but after the jerk I will shift into 3rd and it will haul a**. I'm very confused. These are the new parts I have on it.

TPS
EGR and sensor(took back sensor because there was no difference )
O2 sensor
Map sensor
Brake booster
Radiator
Iac
Cleaned the throttle body very well
Air filter

I ran the codes and I got 33 but I replaced the egr and there was no difference at all.

Someone please help before I go crazy please.

Also, the check engine light will come on but go away when I hit the gas just a little bit then come back on???? Anyone?.
Possibly the ECT. (Temperature sensor)
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