Rough Idle and Engine Surge Under Load

[ERUSH97XLT]

Ok everyone! Sorry for the rather late reply. My explorer is still having issues, although some symptoms have changed:

1. Rough idle still exists
2. Driveability issues seem to have gone away after several doses of HEET for the past few months. I guess water got in the system. Thanks for that solution, Bubba!
3. My CEL is on now. Its the P0171 code: "System Adaptive Fuel too Lean (Bank 1)".

I've googled around for solutions to these issues. Here's what I've come up with:

1. Common causes for the P0171 are due to dirty MAF sensors and vacuum leaks. Based on my previous posts, I have no vacuum leaks and my MAF sensor was freshly cleaned.
2. Another cause I found is a faulty DPFE or EGR. Earlier, James seems to agree. This seems like a likely culprit becuase of my poor idle and previous driveability issues.
3. A "last resort" cause could be a malfunctioning oxygen sensor that "tricked" the PCM into thinking it was running lean. This seems unlikely (or is it?) because of my driveability issues.

I think my next course of action will be to replace the DPFE. It seems like the most likely cause of my explorer's problems. It's relatively cheap (~$50) and if its not the cause, I guess that's one less thing to worry about down the road.

What do you all think? Anything else come to mind? Any input is appreciated!

 

[96eb96]

Ok everyone! Sorry for the rather late reply. My explorer is still having issues, although some symptoms have changed:

1. Rough idle still exists
2. Driveability issues seem to have gone away after several doses of HEET for the past few months. I guess water got in the system. Thanks for that solution, Bubba!
3. My CEL is on now. Its the P0171 code: "System Adaptive Fuel too Lean (Bank 1)".

I've googled around for solutions to these issues. Here's what I've come up with:

1. Common causes for the P0171 are due to dirty MAF sensors and vacuum leaks. Based on my previous posts, I have no vacuum leaks and my MAF sensor was freshly cleaned.
2. Another cause I found is a faulty DPFE or EGR. Earlier, James seems to agree. This seems like a likely culprit becuase of my poor idle and previous driveability issues.
3. A "last resort" cause could be a malfunctioning oxygen sensor that "tricked" the PCM into thinking it was running lean. This seems unlikely (or is it?) because of my driveability issues.

I think my next course of action will be to replace the DPFE. It seems like the most likely cause of my explorer's problems. It's relatively cheap (~$50) and if its not the cause, I guess that's one less thing to worry about down the road.

What do you all think? Anything else come to mind? Any input is appreciated!

Rough idle when cold and a lean code is probably trashed intake gaskets. When the engine warms up metal expands and the crappy gasket can make a seal. Not uncommon for our engines at high mileage. There are upper and lower gaskets. I bet its the upper but you should probably do both. There are threads here how to do it. Not a terrible job.

I would spend money on the gaskets before the DPFE.

 

[stang 1989]

i had the same problem with mine i ended up having two cracked plugs (the porcelin)

 

[ERUSH97XLT]

Rough idle when cold and a lean code is probably trashed intake gaskets. When the engine warms up metal expands and the crappy gasket can make a seal. Not uncommon for our engines at high mileage. There are upper and lower gaskets. I bet its the upper but you should probably do both. There are threads here how to do it. Not a terrible job.

I would spend money on the gaskets before the DPFE.

If my intake gaskets are cracked and leaking, wouldn't I have a vacuum leak? I tested for leaks with both a cold and warm engine. The gauge was steady at about 20-in. Hg in both scenarios. Could cracked gaskets cause a leak without any noticeable indication on the vacuum gauge?

All the sparkplugs were fine, so I'm ruling that out. That was the first thing I checked; I have had broken ones before.

Thanks for your input! What does anyone else think I should do?

 

[96eb96]

If my intake gaskets are cracked and leaking, wouldn't I have a vacuum leak? I tested for leaks with both a cold and warm engine. The gauge was steady at about 20-in. Hg in both scenarios. Could cracked gaskets cause a leak without any noticeable indication on the vacuum gauge?

All the sparkplugs were fine, so I'm ruling that out. That was the first thing I checked; I have had broken ones before.

Thanks for your input! What does anyone else think I should do?

How many miles on your truck?

Can you read the BARO parameter off you MAF sensor? This will give you a health reading on your MAF. Cleaning isn't always the answer.
http://www.performanceprobe.com/ind...rmanceprobe.com/misc/tsb.php?article=98-23-10

What are your fuel trims?

From what I heard about the gaskets its very subtle and just enough to cause rough idle and codes. A few extra grams of air is hard to see on a vac gauge.

Maybe try disconnecting the DPFE, or plug the vacuum line to the EGR. Yes you will get a code but that may eliminate the EGR system as a problem. I have a car now with a plugged EGR tube and there are no issues except for a code.

Also, I would like to know the extended OBD-II info from the lean code. The scanner should report that. What engine temperature did it happen at? What RPM?

I'm also curious to see the resolution. Keep the suggestions coming!

 

[ERUSH97XLT]

Interesting info, 96eb96! Here are some answers, comments, and questions regarding your post:

1. My explorer has 98,500 miles on it.
2. How do I read the BARO parameter off the MAF? From your link, BARO readings vary with the Hz signal. I take it the average Multimeter will read frequency as well as voltage?
3. What are fuel trims and how do I measure them?
4. I got the code read by borrowing Advanced Auto's code reader. It gave me the numerical code, P0171, and the generic description, "System Adaptive Fuel Too Lean (Bank 1)". It didn't give any further information beyond that.
5. I'll mess around with the DPFE and EGR and see what I come up with. I should let you know the results by tomorrow or the day after.
6. Your link suggests unplugging the MAF sensor to see if the driveability symptoms go away. I guess I could try this to see if my MAF sensor is faulty (but wouldn't I get codes for this??).

What do you all think? Anyone else want to chime in and suggest something?

Thanks for the input!

 

[96eb96]

Interesting info, 96eb96! Here are some answers, comments, and questions regarding your post:

1. My explorer has 98,500 miles on it.
2. How do I read the BARO parameter off the MAF? From your link, BARO readings vary with the Hz signal. I take it the average Multimeter will read frequency as well as voltage?
3. What are fuel trims and how do I measure them?
4. I got the code read by borrowing Advanced Auto's code reader. It gave me the numerical code, P0171, and the generic description, "System Adaptive Fuel Too Lean (Bank 1)". It didn't give any further information beyond that.
5. I'll mess around with the DPFE and EGR and see what I come up with. I should let you know the results by tomorrow or the day after.
6. Your link suggests unplugging the MAF sensor to see if the driveability symptoms go away. I guess I could try this to see if my MAF sensor is faulty (but wouldn't I get codes for this??).

What do you all think? Anyone else want to chime in and suggest something?

Thanks for the input!

Need a very capable scanner to read BARO, trims and extended info. I can give you a link to one for around $120 bucks that works with a laptop if you are interested. It would probably cost around there if you had a pro diagnose it. This equipment has a learning curve but its very good.

Fuel trims are the compensations your computer makes for excess air or fuel. If you exceed a threshold the code you mentioned is set P0171. There are short and long term trims, corresponding to sudden events or consistent behavior over time, respectively. Trims could act as a very sensitive vac gauge...using your o2 sensors to read excess air. For example, you may see short term trims change sightly when cold if you spray carb cleaner under the black intake (maybe, but you get the idea).

The scan tool can also look at oxygen sensors and graph their activity. Sometimes they cause issues without throwing a code. I would not say to replace them you see them on the scanner.

These are things a pro would look at if you had a diagnostic.

 

[ERUSH97XLT]

Thanks for the info 96eb96!

I probably won't buy a sohpisticated scanner. It makes more sense to me just to replace the d*** MAF sensor for the price of the diagnostic equipment

I do some simple driving tests with the MAF sensor and EGR unhooked and get back to you.

Again, thank you. If anyone else has any suggestions, feel free to post your thoughts.

 

[ERUSH97XLT]

I rechecked the vacuum with a gague before unbuttoning the DPFE. Before I was a bit brief in telling EXACTLY what it showed. Here are the results:

1. "Smooth Idle" (between rough spots) showed a steady reading (absolutely no movement whatsoever) of 20-in Hg.
2. "Rough Idle" (RPMs dropped slightly and the car shakes slightly) showed a steady reading of 19-in Hg.
3. "Rough Idle" pulses occured erradically about every second or so.
4. Measurements were taken while the engine was warm so as to eliminate the automatic choke as a confound.

I guess before what I described as "steady" and "about 20-in. Hg" was actually the above description.

Could this be a slight leak due to the intake gaskets?

 

[ERUSH97XLT]

Ok. I unplugged the DPFE and went for a few drives. Oddly enough, It didn't throw any codes... In both conditions, the engine was started cold and completely warmed up while driving. The rough idle still exists. I assume this test rules out the EGR and DPFE?

Any more thoughts on my more descriptive vacuum readings? I REALLY dont want to tear into the engine too much until spring when it warms up.

Any help is appreciated! Thanks again!

 

[team]

no, you didn't rule out a leaking egr valve (pintle stuck open a little). To do that, do what I did. Take an aluminum drink can and cut out a small square of it. THen slide that between the egr valve and intake tube that runs up to your intake manifold. There are two bolts between these two objects, loosen them up, there is a gasket between them so leave it there, and slide the aluminum in there to block egr flow.

 

[ERUSH97XLT]

Good tip, team!

I'll try that tomorrow and get back to you.

Any more tips?

 

[96eb96]

You know you can manually operate the EGR using a vac pump. To simulate a stuck pintle, try a very slight vac (8 hg fully open BTW, 1hg for this), to get it off its seat and see what kind of effect you get.

What about snugging up (just a bit) the upper intake gaskets. What do others think?

 

[team]

I will tell you what i have been doing this past week on tracking down my idle missfire with a 170,000 96 ohv sport i just got. I have talked to most people who seem to think it is a leaking intake gasket, but I am not to sure especially after what I found today. First let me tell you what I have tested. I have a genysis scanner and I can see the misfires on screen and feel them. All of the cylinders misfire, but 1,2,3 do it the most. Then 4, 5 and 6 in that order 99% of the time. And when I talk misfires I mean the worse cylinder can get 90,000 plus misfires in a 5-10min. idle session, with the others close behind. But, i have no check engine light on and no stored codes, but I dont like how it feels. ALso, my long term and short term fuel trims are well within normal range.
So i started checking things:
1. plug wire resistance, as well as spark test
2. coil pack checked (and changed out with another working one)
3. new plugs
4.compression test
5.leak down test
6.plugged off all vacuum ports on the manifold
7.fuel pressure test
8.fuel injector pressure drop test at 3 different pulse settings on every injector and all of them dropped within .5 psi on every setting
9.egr test with vacuum pump and completely blocked with drink can
10. upper intake gaskets replaced
11.seafoam and water in engine to clean out carbon
12.new fuel filter
13.carb cleaner sprayed for intake leaks
14. unplugged maf sensor to see if it is causing prob. but its voltage for load and rpm check out fine on scanner live datastream
15. new iac gasket
16. And finally today i took off the lower intake manifold and found the most god awful amount of carbon in the intake ports I have ever seen! The back of the valves looked good but the intake ports were covered. And guess which ones were the worse, in this order, 123456, that just happens to go with where I get my most misfires in order. So i started scraping and vacuuming the chunks with the wetdry vac as I went. My only conclusion, which i have read before, is the carbon likes to absorb some of the gas as it is sprayed and causes lean misfires. The car drives fine and sets no codes, but idles to rough for my liking because of misfires. Now maybe another culprit could be the lower intake gaskets I am going to replace, but i feel like most of it is because of the carbon.

 

[96eb96]

I will tell you what i have been doing this past week on tracking down my idle missfire with a 170,000 96 ohv sport i just got. I have talked to most people who seem to think it is a leaking intake gasket, but I am not to sure especially after what I found today. First let me tell you what I have tested. I have a genysis scanner and I can see the misfires on screen and feel them. All of the cylinders misfire, but 1,2,3 do it the most. Then 4, 5 and 6 in that order 99% of the time. And when I talk misfires I mean the worse cylinder can get 90,000 plus misfires in a 5-10min. idle session, with the others close behind. But, i have no check engine light on and no stored codes, but I dont like how it feels. ALso, my long term and short term fuel trims are well within normal range.
So i started checking things:
1. plug wire resistance, as well as spark test
2. coil pack checked (and changed out with another working on)
3. new plugs
4.compression test
5.leak down test
6.plugged off all vacuum ports on the manifold
7.fuel pressure test
8.fuel injector pressure drop test at 3 different pulse settings on every injector and all of them dropped within .5 psi on every setting
9.egr test with vacuum pump and completely blocked with drink can
10. upper intake gaskets replaced
11.seafoam and water in engine to clean out carbon
12.new fuel filter
13.carb cleaner sprayed for intake leaks
14. unplugged maf sensor to see if it is causing prob. but its voltage for load and rpm check out fine on scanner live datastream
15. new iac gasket
16. And finally today i took off the lower intake manifold and found the most god awful amount of carbon in the intake ports I have ever seen! The back of the valves looked good but the intake ports were covered. And guess which ones were the worse, in this order, 123456, that just happens to go with where I get my most misfires in order. So i started scraping and vacuuming the chunks with the wetdry vac as I went. My only conclusion, which i have read before, is the carbon likes to absorb some of the gas as it is sprayed and causes lean misfires. The car drives fine and sets no codes, but idles to rough for my licking because of misfires. Now maybe another culprit could be the lower intake gaskets I am going to replace, but i feel like most of it is because of the carbon.

whoa...there are cases where carbon like that holds valves open. Such severe carbon is usually happens with the 50K gem that you buy from grandma who just drives to church every Sunday morning. Some spirited driving can help that situation.

It can also be from a previous owner with bad 02 sensor holding the system rich for 10's of thousands of miles...keep ignoring the check engine light!

ERUSH97 would need a scanner capable of seeing misfires though to come to that conclusion. Anyway, tearing into the engine to change gaskets will reveal the carbon. The EGR maybe is something to check too.

 

[ERUSH97XLT]

Now that I think of it, there may be a simple solution to all this mess.

1. When taking off the throttle body to clean it (as per my earlier posts) I noticed the absence of a throttle body gasket. It struck me as a bit odd, but I'm unaware of anyone needing to take it off. This may be a source of a slight vacuum leak.

2. Same situation when I removed the IAC for cleaning. Again, no gasket. Again, odd.

I browsed around my Haynes manual and for both jobs (throttle body and IAC removal), it mentions gasket replacement (O-rings for IAC).

Could this be the elusive problem? I sprayed around these areas with starting fluid and didn't detect them as the source of a vacuum leak. If not, I should put gaskets in their proper place for good measure.

What do you all think?

 

[team]

there were probably gaskets there, just o ring style ones and you didn't notice them.

Also, if you are really trying to save some money just swap the bank 1 and bank 2 o2 sensor and look for you lean bank code to follow. If your code now goes to bank 2 then you know your problem is just a bad o2 sensor.

 

[ERUSH97XLT]

I would've done that, but both bank codes came on (P0171 & P0174) a few days ago.

 

[alohamonte]

I just replaced my IAC last week and the replacement part included a paper gasket. I believe you can order the gasket separately.

EDIT: I should add that when I removed the old IAC, there was no paper gasket.

 

[team]

I would've done that, but both bank codes came on (P0171 & P0174) a few days ago.

you need to find someone with a good scanner and look at the live datastream. So you can see you fuel trims, misfires, and maf. data to get a decent idea of what is going on.
where are you located?