Rough Idle and Pulling 3 Codes

[aeraceranthony]

1994 3.0L Auto 80,000 miles
Pulling 3 codes from a check engine light on the ignition only:
157 (MAF sensor circuit below minimum voltage)
335
337 (EVP or DPFE circuit above maximum voltage)

Car is running really rough. Idle is about 650RPM. Is the MAF bad? I cleaned it and no such luck. All the connector pins are good.

What is 335?

What does 337 mean?

Thanks.

 

[graff104]

according to this http://www.therangerstation.com/tech_library/3digitcodes.html

157 (R,M) Mass Air Flow signal is/was low or grounded - MAF
335 (O) EGR feedback signal is/was out of range - EVR or PFE
337 (O,R,M) EGR feedback signal is/was was high - EVR

EGR problem? thats my hunch

 

[aeraceranthony]

I have a used MAF on its way so hopefully that will clear the MAF probelms.

What I can't understand is the rough idle. Its dragster like.

What would cause the EGR to send such high singals to even be out of range. When I replaced the muffler with a flowmaster, I believed they welded a tab to the chassis from the muffler. Would that throw it off?

 

[fastpakr]

Are those codes listed in the sequence output by the computer? All KOER, or what?

 

[JOKER86]

I looked at alldata and it says the 335 is DTC 335 Exhaust gas recirculation valve pressure sensor voltage higher or lower than expected during KOEO self-test. DTC 337
Exhaust gas recirculation valve sensor circuit above maximum voltageDTC 157
Mass air flow sensor circuit below minimum voltage.....my thoughs are that the egr could be stuck open causing air to get in to the intake and bypassing the MAF and at the same time it is exhaust gas so its causing a rough idle, i would recomend pulling the egr valve off and look to see if it is frozen/stuck open. another thing to look for would be lines going to that system, inspecting for holes, tares or cuts. and it could just be the DPFE has gone bad...another great ford design

 

[fastpakr]

Really need to know exactly how these codes were listed.

 

[aeraceranthony]

they were listed as 335, 157, 337 with car on but engine not running(ignition switch all the way before cranking the motor)

 

[fastpakr]

Some of them had to have been stored codes. Was 335 KOEO and the rest continuous memory?

 

[aeraceranthony]

I want to say yes because after the 335 the scanner paused and then beeped once and paused for a while and then did the 157 and 337.

 

[fastpakr]

OK, that helps a lot. You can completely ignore the continuous memory codes for now. You need to get past KOEO and KOER before those become relevant. Start with checking the two vacuum lines going to the DPFE valve. Verify that each is free from obstructions, and replace them if necessary. Also, measure the voltage between the Brown/White (VREF +) and Gray/Red (Signal Return -) wires at the sensor with the ignition on. If voltage is between 4 and 6 volts, replace the DPFE sensor, then clear the continuous codes and run KOEO. If it's outside of that range, post back and I'll grab the next few steps for you.

 

[SixFoFalcon]

FWIW, swapping the DPFE is dead simple and pretty cheap, too. Probably a good place to start just for those reasons.

Then do the brain-drain routine and see if any codes come back over the next 100 miles or so.

 

[fastpakr]

While it's very likely that it's bad, why in the W@#$)%(@#$ would you replace it without taking five minutes to test it first? Money must come a lot more easily to you than the rest of us.

 

[SixFoFalcon]

Well considering the track record of the DPFE on this application, plus the fact that there is at least one code that could be attributed to a faulty DPFE, it's hardly a crapshoot. Like I said, the part isn't that expensive, and it takes all of 2 minutes to replace it. Yes, by rights, you should always be absolutely certain of the exact problem before you start fixing things that might not be broken, but there's something to be said for playing the odds and, in all likelihood, having more time left over for other things.

 

[fastpakr]

If you have a spare DPFE sensor handy, then I understand what you're saying. If not, then it makes no sense whatsoever. You can spend 5 minutes or less testing, or you can spend half an hour driving to a store to buy a $60 sensor that you may not have needed in the first place. Which one is quicker and cheaper?

 

[SixFoFalcon]

I see your point, but I can order the part from RockAuto in 60 seconds. Didn't realize they were so much more expensive for the '94s... that does change things a bit (but not much.)