Try again... Running rough

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Neilster

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I'm having an intermittent running rough conditon at lower RPM's that has just started over the last two days. No Check Engine light - yet. Surging seems to be a condition coincident with the problem as well. Could be a contributor or other intermittment problem. Seems to be worse when engine is cold.

So far:
1) Given the change in temperature and wet weather, I added some gas line treatment to get rid of any moisture in the fuel.
2) I also thought I'd check the fuel pressure, so I went out and bought a fuel pressure tester. I thought I'd check it when it's running ok so I have a benchmark to compare to. Key On, engine not running is 38 lbs. Engine running 30 lbs. Are these within normal parameters? I think so.
3) I have an OBD-II tester which I will now keep handy to plug in should it start to happen again in case it throws some codes without a Check Engine condition being set.
4) I'm also going to toss in some Lucas fuel conditioner in an attempt to clean the fuel injectors.
5) I believe that boots and coils are ok. Codes should confirm if it throws codes.
6) Charging system seems ok. I'll monitor alternator output as well as it is original.
7) MAF was cleaned earlier in the summer (thanks Driller).

Other note: Engine has 230K Km's on it. Am I on the right track or any other suggestions?
 
Driller recommended MAF clean. I added this as well as something done earlier in the summer when I had the valve cover gaskets changed, spark plugs changed and a couple of boots replaced. I don't think I changed all boots. I'll check the invoice.
 
Some more data

Some more data

Added the injector cleaner this morning and topped up the fuel. Car ran no problems for 15KM @ 115 KmH. Then noticed the stumbling start again. I had the scanner connected and trapped a P0701, Bank 2 Too Lean. Cleared it. Still ran rough off and on. Caught one P301 (cylinder 1 misfire). Only caught it once. Engine was running rough but no codes caught. Hmmm.

I am thinking sticky IAC or fuel pump is on its way out. I haven't had a chance to check the fuel pump pressure yet. Do you see the pressure fluctuate when the pump starts to go? Or does it basically read ok until it finally fails?
 
Have you ever replaced the oxygen sensors? How many miles on the car? The sensors could be sending wrong signals to computer.... or maybe the cats are starting to clog up too.....
 
Prob past the time to replace the oxy sensors....and about the time for the cats to start to go.....I'd replace the oxy sensors first.
 
Thanks guys. The car has around 135 - 140K miles I spoke to a reputable service center (works almost exclusively on Mustangs). I think I'm dealing with multiple problems consistent with the age of the car. Oxy's are on the list, IAC (surging), possible flakey coil(s). He said the fuel pump is not the issue. It would bog or fail completely not cause sputtering/ stumbling. So, I have some decisions to make. Good input guys. I appreciate it.
 
Neilster said:
No Check Engine light - yet.
Click to expand...

Remember, just because there is no light, doesn't mean there are no codes stored. ALWAYS check for codes even if there is no CE light, expecially since you have one handy. :)

Neilster said:
I had the scanner connected and trapped a P0701, Bank 2 Too Lean. Cleared it. Still ran rough off and on. Caught one P301 (cylinder 1 misfire).
Click to expand...

Bank 2 is too lean because you are running rich on the other side due to the Cyl #1 (Bank 1) misfire. First thing you need to do is pull the #1 coil/boot/plug and see what you got going on. While you're in the area, swap everything directly with the #2 stuff and then check for codes again. If the problem changes cylinders (i.e. cylinder #2 misfire) then you'll know you have a bad boot or coil.

Neilster said:
I think I'm dealing with multiple problems consistent with the age of the car. Oxy's are on the list, IAC (surging), possible flakey coil(s).
Click to expand...

The shop you went to is on the right track, but here is what I think. First off, the surging is GOOD. That means the IAC valve is working appropriately and its having to constantely adjust with the intermittant cylinder #1 misfire. Basically the car idles smooth and then rough, smooth and then rough, and the IAC valve is constantly adjusting to that giving you a surging sensation.

Basically, if you change the O2 sensors and the IAC valve, you're still going to have a CYLINDER #1 MISFIRE!!!!! The engine spark is the beginning of the system, so to speak, and you want to address that first. You wouldn't put new oil in your engine before you drained the old stuff would you? :)
 
Very good logic. Now that I understand the system better, I had arrived at the same conclusion. Thanks to the team for your input. Will keep you posted on results. I'm also glad I invested in the code scanner as it was very helpful in this triage dialog.
 
Update - Misfire, Poor Running

Update - Misfire, Poor Running

Update: Decided to replace the Coil Pack on cylinder 1 on Saturday AM as suggested here. I had a spare used one on hand. It is Tuesday afternoon and the problem has not come back yet. Although it did cold surge yesterday, but it was doing that once in a while for the last year or so. IAC probably needs to be replaced. Anyway, so far so good as far as the stumbling poor running goes. Wish me luck.
 
Sweet! The surging still may be the IAC valve, but on your car its SUPER easy to change so it may be worth investing into.
 
You bums jinxed me. My car is starting to surge now, really lightly though at like quarter throttle. I have new TPS sensor and IAC valve I didn't throw on it last time I replaced the dpfe, egr valve, and vacuum regulator. Going to purchase oxy sensors and do the remaining 3 things (iac,tps,and sensors) at the same time. I already have new coil packs etc etc so I am really thinking it's going to be the oxygen sensors.

Questions: I couldn't remove the screw that hold the tps to the Throttle body last time and was afraid of stripping it, even after soaking it with a little PBR. Any suggestions?

How many oxygen sensors? 2 or 4 ?
 
Lol, you jinxed yourself by NOT replacing the TPS and IAC valve!!! :D

Those TPS screws SUCK. I used vice grips on mine before I stripped the phillips head out. You can also try putting the screwdriver in the screw and hitting it with a hammer to break the threading free, then turn, then tap some more, then turn. Repeat as necessary.

2 O2 sensors but you're wasting your time on those. :D Its your TPS sensor that is bad, causing a "surge" or a "flat spot" in the throttle.
 
Yeah and If I get a new throttle body, then it comes with the tps. Am I better off snagging one from the yard?
 
No, its easy to get off, just grab the screws with vice grips. Remember, you can break the old TPS, just don't damage the screws.
 
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