2g rough/lean idle on startup first 3-5 min

[re-rx7]

Noticed this happening the other day. When i start my car whether it be cold start or warm it will shake/vibrate and the wideband reads off the guage lean. If I let it sit there after about 3-5 minutes idling rough/lean it will rev up on its own and go back to normal fuel trims and everything and i can drive and boost just fine. In this first start up period if i attempt to drive it will bog down and attempt to die unless i floor it then it will bog dwn (lean) and take off after a sec. No part throttle either in this period with out bogging.. If i wait, like mentioned above, it does just fine as long as i dont kill it then it starts all over again.

Really at a loss right now. It was sudden issue. No problems before this.

 

[90 Talon AWD]

I have the exaxt same problem

 

[re-rx7]

I have no clue what it could be.

 

[kchaazz]

What fuel pressure regulator are you two guys with the issue using? I was using an EL-CHEAPO AFPR, and my car did the same thing yours is doing now. I swapped the regulator for a quality pice, and my car has been perfect ever since!

 

[re-rx7]

OEM Fpr, 142k miles on a wally 255. If it failed how would it fail in a way that could cause this?

 

[007jimmy]

The stock FPR can't handle the pressure from the 255 pump. Its overrunning your regulator at idle and part throttle. How old is your o2 sensor?

 

[re-rx7]

Yea i ve heard that but i spoke with RRE and alot of those guys are running street cars without them A Afpr. The car ran fine before this way for months. O2 sensor maybe has 1k miles on it. If i was over running it, it would be running rich not lean to the point of dying.

Edit: went out and pulled the FPR vaccuum line and idle did not change. I pulled it off and used my finger to plug off the vaccuum from the manifold leaving just FPR nipple exposed. The idle did not change.

 

[007jimmy]

Yea i ve heard that but i spoke with RRE and alot of those guys are running street cars without them A Afpr. The car ran fine before this way for months. O2 sensor maybe has 1k miles on it. If i was over running it, it would be running rich not lean to the point of dying.

I understand what you are saying. I did it too. I got the pump before the AFPR and I didn't have no problems at the time, I ran it for months like that. As for the o2 sensor I had some issues with rough starts and it was because my o2 was lazy to cycle. When I logged it with link it would stay flatlined for sometime .02-.04v.. It would finally cycle after a few mins. I changed it out and haven't had no problems since. Switched from a bosch to a OE denso unit. No CEL came on at all.

 

[re-rx7]

I understand what you are saying. I did it too. I got the pump before the AFPR and I didn't have no problems at the time, I ran it for months like that. As for the o2 sensor I had some issues with rough starts and it was because my o2 was lazy to cycle. When I logged it with link it would stay flatlined for sometime .02-.04v.. It would finally cycle after a few mins. I changed it out and haven't had no problems since. Switched from a bosch to a OE denso unit. No CEL came on at all.

Interesting thats what i replaced my o2 sensor with was a bosch. It actually ran alot better after putting this one ina nd then one day it just started doing this. I may replace the bosch with another since it will still be under warranty. If it changed the problem i will buy a OEM denso. I dont have a cell at the moment.

 

[kchaazz]

The stock FPR can't handle the pressure from the 255 pump. Its overrunning your regulator at idle and part throttle. How old is your o2 sensor?

It is not that the stock fpr cannot handle the pressure, it is that the orifice in the stock fpr is so small, it cannot flow enough fuel to handle the sheer volume of fuel the 255 is delivering, and it causes fuel pressure to rise and this causes a rich idle and cruise condition. Also, overrun is more common in 1G cars because the 1G turbo FPR has a base fuel pressure setting of 37.5 psi, and the 2G has a base setting of 43.5 psi, so the 2G FPR is more difficult to overrun. The OP and second poster are having issues with running lean on startup, not rich, therefore, there is an issue with fuel delivery. Also, the ECU doesnt even use O2 sensor readings to adjust fuel delivery at all until the motor reaches a certain temp, and uses a rich fuel map and high idle to bring the cold motor to operating temp as soon as possible to get into optimum operating range, so the O2 sensor is not the problem here, and bad O2 sensors typically cause rich conditions, rather than lean conditions. To the OP, one thing I will suggest is since you are on the stock FPR, which rarely ever goes bad, perhaps the cause of your issue may be the coolant temp sensor. Can you log your coolant temp at startup and tell us what the logger says?

 

[re-rx7]

I unfortunatly do not have a log. Are you saying that the Coolant temp sensor may be sending false readings to the ECU? Keep in mind that when it started doing this i was driving down the hwy with the engine at operating level.

 

[kchaazz]

I unfortunatly do not have a log. Are you saying that the Coolant temp sensor may be sending false readings to the ECU? Keep in mind that when it started doing this i was driving down the hwy.

Now, if youre driving down the hwy, Im not so sure what would cause your lean condition, other than a huge vacuum leak, or problem with your fuel pump, dirty injectors, etc. Regarding O2 sensors, the thing about bad O2 sensors is that they dont cycle properly, or at all, so instead of voltage consistently fluctuating between .3- .7 volts (on a healthy narrowband sensor) at idle and cruise, you end up with a static .1 or .3 (just for example) volts being sent to the ecu, where 0.0 volts is leanest and 1.0 volts is richest, a .1 volt reading will cause the ECU to dump as much extra fuel in as it can in an effort to raise the O2 sensor voltage, resulting in a rich condition.

 

[re-rx7]

Thats the weird thing. If i start it again while its still warm it does the samething as when its cold. 3-5 minutes of lean, rough low rpm idle then back to normal. If i drive it before it goes back to normal it will bog out ,stutter, until i floor it then it will bog and takeoff Confused!

 

[007jimmy]

It is not that the stock fpr cannot handle the pressure, it is that the orifice in the stock fpr is so small, it cannot flow enough fuel to handle the sheer volume of fuel the 255 is delivering, and it causes fuel pressure to rise and this causes a rich idle and cruise condition.

Which still means the stock FPR can't handle the 255 no matter how you break it down. The OP, where is your WB located? Exhaust leaks can cause false readings on the sensor. Do you have boost leaks??
http://www.dsmtuners.com/forums/newbie-forum/424568-wb-issues-lean-theres-no-way.html

 

[kchaazz]

Which still means the stock FPR can't handle the 255 no matter how you break it down. The OP, where is your WB located? Exhaust leaks can cause false readings on the sensor. Do you have boost leaks??
http://www.dsmtuners.com/forums/newbie-forum/424568-wb-issues-lean-theres-no-way.html

Yes, the FPR can be seeing some overrun, but the higher base pressure of the 2G unit makes this a rare instance, and many people years ago were using 1G non turbo FPRs, which also have a higher base pressure of 43.5psi, on the turbo cars to negate overrun with much success, but the OP is running lean, not rich, which is counterintuitive to the FPR being overrun. Also, while pre O2 and wideband O2 exhaust leaks will lead to innacurate readings, his wideband is reading absolutely correct when it is reading lean because the driveability of the car reflects this.

 

[TNTDSM7777]

I have been having this same problem as well. Check the timing. I found that my timing was maybe 5 degrees retard. Haven't put it back together yet, but hopefully that solves the problem

 

[re-rx7]

I have been having this same problem as well. Check the timing. I found that my timing was maybe 5 degrees retard. Haven't put it back together yet, but hopefully that solves the problem

Car runs fine when after the 3-5 min mark.

 

[kchaazz]

Car runs fine when after the 3-5 min mark.

You know, I was just discussing fuel filter issues with another member, and it just occured to me that perhaps your fuel filter is clogged and in need of replacement. Think about it, it makes perfect sense that a dirty, partially clogged filter would cause the pump to have to work harder at initial startup in order to get your fuel flowing properly to get the car running correctly. If your filter hasnt been replaced in a while, try this to see what happens, theyre cheap and easy to replace and you need to be looking to your fuel delivery system to find the problem regardless

 

[re-rx7]

I thought about that. I replace the filter about 10k miles ago. Also under WOT it would be extremely noticable if it was clogged but the AFR's are right where they should be. Plus killing it and starting it right back up wouldnt be a problem. Its almost like the Car forgets what it was doing.

 

[TNTDSM7777]

I replaced the filter on mine. Didn't change. I also put a new coolant temp sensor in. Since I thought it was reading open loop and closed loop differently

 

[re-rx7]

Im thinking o2 sensor. if the o2 sensor is bad the ecu will have to learn the o2 upon every start and slowly compensate for what it thinks to be a lean mixture by flowing more fuel a little at a time until it get the right amount/map it deems as neccesary. What you guys think? Plus my o2 is under warranty so it wont cost a dime to check.
I have a log o r2 now. I dont know how to get them to post. I can email them to someone if they want to post them. It shows my coolant temp to be in the 90's and my car was idling for at least 20min.

My ####ing maps are all messed up!

 

[re-rx7]

Ummm pretty sure thats not it. thanks though.

New o2 sensor=solved problem, however i do not think it was the o2 sensor at fault. Upon closer inspection of the wires connecting the o2 sensor i notice some were melted together. I ssuspect it was a short in o2 circuit wreaking havoc on ecu sytem.

 

[newtodsm97gst]

Ummm pretty sure thats not it. thanks though.

New o2 sensor=solved problem, however i do not think it was the o2 sensor at fault. Upon closer inspection of the wires connecting the o2 sensor i notice some were melted together. I ssuspect it was a short in o2 circuit wreaking havoc on ecu sytem.

did you fix the problem? my car doing the same thing..

 

[mitsubishikid]

I had a similar thing happen to me after I had my 190 lph fuel pump installed, at first I had no issues, but after a few months it started happening, i'd start it it ran then killed several times till it wormed up, and then it would misfire/bog at around 2500 rpms, if I hit the throttle hard it would stumble till boost was hit, I borrowed an idiot rich lean gauge from a friend, and it read lean, so I pulled my f.p.r return hose off and pointed it over a bucket, had someone else crank the engine over... no fuel?

I thought back as to what might have been done to the fuel system, I knew I had a new fuel filter installed, so then I logically pulled the fuel pump out of the tank, and sure enough the fuel pumps o ring had popped off and it was spraying fuel into the tank instead of supplying the motor, I re-installed it,put the pump housing back in, it only took ten minutes and problem solved, I also used an ohm meter on my injectors all were good so I figured look somewhere else hope this helps other dsm'ers out there with this issue.

here is a list of things I checked before coming to the above mentioned conclusion not in any particular order mind you.


the injectors should all read around 0.20 to 0.30 anything too far from this range should be replaced.

also check spark plugs condition/and the wires.

the coil pack and wires should also be tested.

the c.a.s and its wiring should also be checked.

run a compression test.

ecu and its wiring.

check transistor and wiring.

coolant temp sensor and wiring.

02 sensor and wiring.

thermostat.

alternator and its wiring .

do a boost leak test, and check the condition of all the vacuum lines.

If all else fails try and remember what you last serviced on your car it could lead you to something you might have forgot, or over looked, or did wrong, hey were all human right.

 

[VTDSM28]

vacuum lines, had the exact same problem until i replaced all of them and everything was cracked and dry rotted