BigBirdLS1

I have recently been able to not really drive my car very much at all like >250 miles in 3 months. I got a beater 98 S10 FTW. I have put new K&N filter SLP lid MSD wires and NGK TR6 plugs and a mailorder tune in those 3 months. I have noticed that when I do drive my car when I press the brake to slow down at a stop light or something that the rpms will dip down to idle then go up 300-500 rpms for a second then back to idle and stay there the whole time I am sitting there. My question is that what could be causing this surge.

LS6427

iTrader: (2)

vacuum leak, which could be directly ralated to when you hit the brake pedal.

Check for vacuum leaks.

BigBirdLS1

Should I check just my intake i.e. lid to throttle body or should I check everywhere like all around my intake manifold too. And what is it I should use to check for the leaks just look and feel around or some kind of spray. Thanks for you info.

LS6427

iTrader: (2)

Yes, check everywhere for cracks.

I believe mechanics have guages that can read if there's a leak. But just yourself, you can listen for any sucking noises, check all the hoses like the brake booster line and PCV lines, make sure there's no tears or if they are loose.

You may also have an issue with your IAC valve. (Idle Air Control) If they start to fail they will cause your stalling as well.

BigBirdLS1

Thanks for the info but I don't know where the Idle Air Control is located at I don't really know and if I find a leak say in one of the vaccum lines so I just replace the one line or go ahead and do all of them.

duh

iTrader: (16)

last time I was around an LS1 doing as you described it needed a re-tune. His was saying the maf was bad, and we played with that and started looking into the computer.....turns out it had gotten to a point in the tune and couldn't get out....really weird stuff. Maybe look into that....

BigBirdLS1

Do you mean his SES light was on and the computer was saying bad MAF? If that is the case I have no SES light on so I haven't shown any codes I did run my scan toll anyways and no DTC's came up. I am going to check my vaccum lines for leaks and if I find none I will definitely look into the tune side of it. I sure hope who did my tune will fix it for free if that is the problem thanks for your insight.

1Loudz28

iTrader: (47)

probably the mail order tune....go invest in a real dyno tune

LS6427

iTrader: (2)

Actually, "duh" has some good info.

Before you do anything, clean the MAF. You WILL NOT get a SES light for a dirty MAF. You will also NOT get an SES light when something does fail, our PCM's sometimes just do not show SES lights when they should 100% of the time.

Buy a can of spray MAF cleaner or clean it yourself with alcohol and Q-Tips. But doing it with Q-Tips is a very delicate procedure, its easy to break the sensor wires if you're not careful. Get the spray if you haven't seen it done.

BigBirdLS1

I have an update. I drove my car roughly 50 miles last night. It never surged once and I never tried anything to make it stop. My guess is my PCM had to have time to learn its new parameters or something. Oh well I am glad that is fixed, but maybe I am being paranoid but it seemed like at low rpms it would stumble ever so slightly then once it came up in rpm it would smooth out again. Could it be all along the ever elusive vaccum leak or dirty MAF?