Idle Surge When Coming to a Stop

[MNwe4]

My car has recently developed an idle surge when pulling up to a stop light/sign. The RPMs wander for a bit, enough that it's obvious to anyone something is wrong, then settle out and the car is fine. Start-up, cruising, and rolling into boost is normal. TPS voltage is .42. The surging was noticed after installing a new turbo, welded stock headers, iac angle boss, rjc power plate, brass heater control valve, and fuel filter. Before theses changes the car was fine. Unfortunately the weather has not been cooperating so I haven't been able to diagnose it further. Anyone have ideas on where to look first?

 

[turbojd]

Check for a vacuum leak, or try and reset the IAC.

 

[blackgn1]

You might check the alternator also.

 

[MNwe4]

The IAC might not be a bad one since it was disturbed due to the installation of the Angle Boss. Anyone know if this installation requires resetting the IAC? What are the symptoms of a bad IAC? This seems like a logical place to start.

If it was a vacuum leak, would it smooth out like it does or would it stay idling rough?

 

[chops]

Did you try a relearn procedure with the chip .was the battery diconected

 

[grocerygetter]

i vac leak would continue idling bad. I had the same relearn Q as chops...but also, you try simply cleaning and resetting the IAC.

 

[chops]

Whats your fuel pressure at idle?

 

[MNwe4]

Thanks for the responses guys. The battery was disconnected while we worked on the car so the ecm has re-learned. It was driven three times before I made the post. Every time I pulled to a stop it acted up then went away. Before the IAC was re-installed it was cleaned. I do remember it falling off the work bench, but we looked it over and did not see any visual damage. Hopefully it just needs to be adjusted.

Would a vacuum leak even cause surging, or just a high idle BLM? I know all of the lines are connected and we zip tied every connection just to be sure. I will go over them again though.

 

[MNwe4]

Whats your fuel pressure at idle?

Fuel pressure looked good and responded properly. 42psi line off I believe.

 

[chops]

Am glad it worked out for you

 

[chops]

A vac leak will def cause high blms also a good enough vac leak will def scew up idle and other drivability concerns

 

[drturbo69]

P.m. Sent doc

 

[MNwe4]

Haven't corrected it yet. Now they're predicting snow for tonight. Sheesh. I'll take a look at it this weekend and let you guys know what the culprit was if I figure it out.

 

[84BuickGNYorkPA]

+ 3 or 4 on resetting the IAC, they can be finicky to set. Check this site under basic's Basics (Idle Air Control) Adjustment

Chuck

 

[MNwe4]

Problem Solved

Just to wrap up the thread, resetting the IAC did the trick. It was at 81 at hot idle with the TPS at .42. Setting the IAC down to 25 and the TPS to .46 made a very noticable difference. Below are the rest of the readings off of the scanmaster and the rest of the gauges. Please let me know if any of them seem off, otherwise the car's running great. Thanks again guys.

AF 05
L8 33
BAT 13.7
INT 128
BLM 132
CLT 167
ATS 118
RPM 850
TPS .46
IAC 25

Oil Pressure 27 psi
Vacuum -16 inHg
Fuel Pressure 33 psi line on
AFR 13.6-14.1

 

[84BuickGNYorkPA]

Here is a good link related to the scanmaster readings for your reference Scanmaster Readings Explained just click on the end of the sentence and a pdf will download, open up the download to see the explanations.
TT chips are set up for a base line of 42-43lbs. fuel pressure, line off. I see yours is set lower, usually the car won't be getting enough fuel with it set that low.
Glad resetting the IAC fixed your problem.

Chuck

 

[TurboDave]

Just to wrap up the thread, resetting the IAC did the trick. It was at 81 at hot idle with the TPS at .42. Setting the IAC down to 25 and the TPS to .46 made a very noticable difference. Below are the rest of the readings off of the scanmaster and the rest of the gauges. Please let me know if any of them seem off, otherwise the car's running great. Thanks again guys.

AF 05
L8 33
BAT 13.7
INT 128
BLM 132
CLT 167
ATS 118
RPM 850
TPS .46
IAC 25

Oil Pressure 27 psi
Vacuum -16 inHg
Fuel Pressure 33 psi line on
AFR 13.6-14.1

If you had a powerlogger or direct scan or other tool that would allow you to view your BLM cells, I'd bet a beer you'd see that the difference between cell 0 and cell 1 are probably pretty large, and one them is still trying to learn in. Usually when the idle cells (0 & 1) are at a particularly high or low level, and the ecm has been reset, you'll get the idle surge when one of them is learned and the other isn't quite there yet. It's the idle rpm jumping up and down between the two cells, one rich one lean for example.

 

[MNwe4]

If you had a powerlogger or direct scan or other tool that would allow you to view your BLM cells, I'd bet a beer you'd see that the difference between cell 0 and cell 1 are probably pretty large, and one them is still trying to learn in. Usually when the idle cells (0 & 1) are at a particularly high or low level, and the ecm has been reset, you'll get the idle surge when one of them is learned and the other isn't quite there yet. It's the idle rpm jumping up and down between the two cells, one rich one lean for example.

Ah, I get what you're saying, but the car had been driven 4 times since the ecm reset. Not sure exactly how long the initial re-learn takes, but I didn't think it was that long. I do have a powerlogger and will take a look at it again on Thursday assuming it's done raining by then. Should the two cells be equal, or what should I be looking for? The car is running fine now, but I'm always interested to learn new things.

 

[TurboDave]

Cells 0 and 1 (upper left, and next one to the right) should be very close to the same value.