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  #1  
Old 04-26-2011, 01:58 PM
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1997 E300 CODES P0400/P0120

I just changed all my GP and cleaned the intake manifold EGR and related flaps on the IM. After clearing the codes from that problem I am now getting P0400 AND P0120 with my check light on. It says P0400 is an EGR flow malfunction and P0120 is a throttle position sensor A circuit malfunction. The car starts and idles well BUT upon accelerating it HESITATES with the RPM going up and down by a few hundred. It seems to clear up after 10 minutes or so of driving. But goes back to its old ways once left for awhile and restarted. Anything I should be looking for. Thanks in advance.

Rod

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  #2  
Old 04-26-2011, 02:07 PM
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Location: Walnut Creek, CA & 1,150 miles S of Key West
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Look for loose or disconnected vacuum connections. Start at the EGR.
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Old 04-26-2011, 03:25 PM
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Quote:
Originally Posted by rodm View Post
I just changed all my GP and cleaned the intake manifold EGR and related flaps on the IM. After clearing the codes from that problem I am now getting P0400 AND P0120 with my check light on. It says P0400 is an EGR flow malfunction and P0120 is a throttle position sensor A circuit malfunction. The car starts and idles well BUT upon accelerating it HESITATES with the RPM going up and down by a few hundred. It seems to clear up after 10 minutes or so of driving. But goes back to its old ways once left for awhile and restarted. Anything I should be looking for. Thanks in advance.

Rod
The codes you mention can be caused by any one of a number of sensors. There are the two sensors on the side of the air intake filter box which have the same part number. One controls the resonance flaps, and the other controls the egr valve. On my model, those two vacuum pressure transducers also receive a signal from an intake manifold sensor that is located on the left wheel well, and has a small black rubber hose attached to the intake manifold. Then there is the actual throttle position sensor itself located near the drivers side firewall. You mention that you changed out the glow plugs, and that may have required the crossover pipe to be removed. I changed out my plugs, and when I reinstalled the crossover pipe, one of the small wires connected to the resonance flap control broke, and when I went to start the car, I immediately got a code. Those connection plugs are small and it is very easy to damage the wiring. Along with checking the vacuum lines as already suggested, I would also remove each electrical plug, spray it with electronics cleaner, and reinstall it. Hope this helps...
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Old 04-26-2011, 06:03 PM
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Pull a vac on EGR and make sure it moves. If it does then work your way back from there looking for blockages.
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  #5  
Old 04-26-2011, 08:35 PM
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THANKS guys when I am off this weekend will check all that you mentioned.
Rod
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Old 04-27-2011, 11:35 PM
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It's Something Simple for Sure

If my memory serves me right, the first time I took the intake manifold off I had the same problem and it was simply I forgot to reattach the short small vaccum hose that connects the intake manifold to the MAP sensor which is attached to the "sound wall" by the master cylinder. If the vacuum hose is connected properly I'd still check to make sure the hose or the fitting isn't blocked with muck from your cleaning of the intake manifold or alternatively cracked and leaking.
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  #7  
Old 05-13-2011, 12:22 AM
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Location: Scottsdale AZ
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Talking Hit my issuse dead on the head

Quote:
Originally Posted by pimpernell View Post
The codes you mention can be caused by any one of a number of sensors. There are the two sensors on the side of the air intake filter box which have the same part number. One controls the resonance flaps, and the other controls the egr valve. On my model, those two vacuum pressure transducers also receive a signal from an intake manifold sensor that is located on the left wheel well, and has a small black rubber hose attached to the intake manifold. Then there is the actual throttle position sensor itself located near the drivers side firewall. You mention that you changed out the glow plugs, and that may have required the crossover pipe to be removed. I changed out my plugs, and when I reinstalled the crossover pipe, one of the small wires connected to the resonance flap control broke, and when I went to start the car, I immediately got a code. Those connection plugs are small and it is very easy to damage the wiring. Along with checking the vacuum lines as already suggested, I would also remove each electrical plug, spray it with electronics cleaner, and reinstall it. Hope this helps...

I just had been monkeying with the EGR and Res Flap transducers and vacuum tubing. I could not get rid of my P0400. Then I read this, and popped the hood to find the vacuum tube for the intake pressure sensor rotted. Installed a new tubing and blisssss
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  #8  
Old 06-08-2011, 08:48 PM
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did you ever resolve this issue? If so, what was it?

Thanks in advance!!
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  #9  
Old 12-02-2013, 08:02 PM
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Just to close this thread....it was one of the vacuum lines off of the intake manifold that was not connected. Upon checking the vacuum lines that were accessible some were brittle so all were changed as well....Codes went away.
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  #10  
Old 12-07-2013, 06:57 PM
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I wanted to add my recent p0400 code reading. About a month ago I did a complete Biodiesel Submerge with my entire intake. Upon reassembly and start up, a new check engine code P0400 appeared. I took the intake apart 4 times since trying to get this thing to clear. Cleaned all the parts associated with the EGR system. I noticed that on the cross over tube that the mechanism that controls the flapper had a sudden pause in movement. This was caused by the biodiesel somewhat drying out the plastic and not letting it move smoothly, or even buildup. Check both flappers on the cross over tube and underside of the intake body that they move smoothly. If they don't, in my case it'll pop the code. I also cleaned out all the electronic connections with cleaner. All codes are now gone.

There's some simple tests that can determine basic EGR functioning. I found that collapsing the EGR would cause the engine to slow in speed, signifying proper functioning. There's a number of things that can cause this. Just keep checking and rechecking.

Good Luck to anyone in the future that like me found this thread useful.

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