Recently I've been having 2 strange problems when I first start the car and then after its warmed up at idle.

When I first start the car and drive to work before the car is totally warm, I get a surging sensation from the engine. If feels like the car is pulling timing, sort of. If I drive at a constant speed, say 25mph at very light throttle, it feels like its bucking almost, its very unsmooth. You can physically feel the power come and go, even at 25% throttle. Once the car is all warmed up it goes away completly, but that leads into another little problem I'm trying to diagnose.

The second problem I'm having is my idle is surging, kind of like what would happen on the 1g's. I thought it was a simple misfire at idle because my plugs were gapped too wide (.028 on NGK 7s), so I got new plugs and closed the gap to .025 but that didn't help. This only happens about half the time I'm at idle and its totally unpredictable...

I've tried messing the idle control settings in ECUFlash but no luck.

 

Mods? non-stock injectors?

 

opps, stock injectors. mods are TBE, MBC, drop in, Ebay o2 & FMIC.

 

Your K&N that adds 0 power got oil on your MAF, clean the maf and see if that helps.

 

I agree that you should check the MAF for residue and leaks...

But aside from that, have you actually checked your fuel trims? Sometimes minor mods can throw off your idle and low RPM MAF signal enough to throw off your fuel trims so their way out of range...

Here's an example..

Car is not up to temp, start engine, Catalytic converter and O2 sensor is cold, ECU has to run open loop and either the MAF frequency is very low, or another mod has altered the engine efficiency, therefore its running really lean and idles poorly.. If you leave before the engine is completely warmed up, you'll have a situation where the car is in closed loop, but may not have its trims fully "Compensating" for your airflow, so you can get surging and bucking until the coolant temp comes up and the car is completely operating in closed loop and the short term trims have adjusted.

The other example is when you get surging at 25% throttle, although in reality the open loop transition is around there, its probably again slightly low airflow, so when it steps out of the closed loop to open loop maps, your hitting a load cell that may be a bit lean (you might be able to catch this stuff with a wideband)

There is no easy fix other than obvious things, check for a small vacuum leak, or other leaks letting unmetered air into the engine threfore bypassing the MAF

Since you have very minor mods, I wouldn't recommend altering the fuel tables at idle and low load, but if you cannot find any leaks, and your MAF isn't gummed up with oil, then you can usually force the car to idle in open loop and see if it does the same thing.. If it does, alter your fuel table a bit in ECUFlash for the idle and low RPM so your AFR's are at about 14.7 (it'll probably require adding enough fuel to where your fuel map is around 14.0)

But only do that after your certain its not a problem..

Also, inspect your ISCV, they are known to have problems and either get stuck open or closed, which can alter your idle speed and quality, and in some cases low RPM low load operation. Other than that, you might want to put the stock air filter back in and see if the issue goes away..

 

Sounds like unmetered air to me!

 

Well I boost leak test my car at least twice a month so I can rule that out. I also don't have any oil on the maf either.

As far as unmetered air that is a possiblity I guess... but I don't have that many VAC lines to begin with. And the problem isn't that consistant so I don't know.

My injectors are pretty new (replaced under warranty) and my LTFT are around 4%...

keep those ideas coming please.

 

If its inconsistent check your Idle Speed Control Valve.. I had a friend have one go bad and it caused all sorts of drivability and idle problems.

 

Is the RPM pulsating like 1300 to 1700 every second or two?

I had what I mentioned twice - first time PVC hose popped off, the second time my stepper motor toasted

 

I just double checked the vac lines and gave it another boost leak test... nothing to report.

what its doing is jumping from the normal idle to like 1100-1300, holding that for 10 or so seconds and then going back down to normal idle.

There are only 2 pcv hoses right, the one that pulls air from the intake elbow (connects to the valve cover above the Cam Position Sensor) and the one with the actual PCV valve on the back of the valve cover. both are connected.

How would I go about checking the stepper motor??

 

bump. I've got the exact same problem and I can't figure it out either.

 

Cold start driveability symptom is normal until it the coolant hits normal operating temp.

Idle issue I would go back to stock ISC step maps and start over along with turning the Basic Idle Adjustment Screw clockwise a little to cut down the airflow past the TB.

 

A MAF sometimes just goes bad for no real reason. Try going back to your stock map. If that doesn't improve anything try disconnecting the MAF. If that does improve things then try swapping with someone else's MAF.

 

first thing I tried was flashing back to stock but that didn't work. I'll swap out my MAF for a known working MAF and see if that doesn't fix it.

 

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