i am having a very hard time figuring out an idle surging bug i have guys. I have had an Accel AFPR on the car since practically stock and never had any problems. Fast forward: heads, cam, etc put the car back together and had an idle surge problem ever since. I am pretty darn sure its not a vac line leaking. They have been changed, checked, etc, etc. New injectors, fuel pump, etc all check out good. Car runs awesome cruising or at WOT, but surges about 500-70 RPM at idle MOST of the time. it will also surge at about 1500 while cruising. it seems like it runs out of fuel then comes back to life for a second (plus the A/F guage falls on its face so i know it did go lean for a sec) I think its the FPR b/c i took it apart during the heads/cam swap and inspected it and put it back together (very carefully). I DID notice i put it back together OFFSET by one screw the way it came off. The cap went on 1 click counterclockwise the way it originally came off (my bad), but i dont think that should have affected it. Maybe it did?? The diaphram looked good, etc. So i hook up a vac guage and these are my #'s at idle. I have a pretty steady fluctuation between 10-15 in Vac Hg. For starters that is low compared to the "norm" (17-22 "). So its LOW and fluctuating....ANY TAKERS?? Also, after the heads/cam, i decided to step up to a frsh motor. New everything. I can tell you the intake is sealed, TB sealed, etc etc...its all friggin sealed up!!! still same problem on the new motor. THANKS....(BTW no fuel in the vac line at the regulator) Also, when i check the fuel pressure, the guage goes crazy between 40-90 psi fluctuating like crazy. Nothing changes when i rev it up...it just does it faster and faster (NEW INFO!!) OK guys, well, i reset my min idle air adjustment and the car idles A THOUSAND TIMES better. It is pretty much as good as it can get given the mods. No more surging..idle is nice and steady. Grumpy (member here) was nice enough to check out some Datamaster runs i had and told me my IAC was way too active. So that was the surging issue i guess. HOWEVER.....the FP problem is still there. ANy guage i hook up to the rail shows the FP bouncing like crazy from like 40-80 psi. it seems in syncronization w/ the injector pulses. I was thinking maybee clogged return line?? I dunno, the car runs awesome and feels great. My gut feeling tells me its the regulator still.....need your opinions. Also, as far as the vaccum goes. There is pretty much NO fluctuation now but it is still LOW at idle. Now, i do idle at like 750 rpm so that may be it...just too low of an idle speed. As soon as i bring up the revs...like 850 or more the vac. jumps right up into the "normal " range...so Im not worried about that one bit. Actually, the guage indicates "late timing" , but i tchecked and checked it...unplugged the tan/blk just like usual. If i give it any more timing it runs weird and surges. So what do you think guys???

IAC?

brand new...and the IAC #'s on my scans (DataMaster) look good also

???

Classic signs of a vacuum leak.

Use the water method and pour it around every possible place the leak could be. Use lots of water, not just a mist. When the engine stumbles, you've found it.

Runner to plenum gaskets being put on the wrong side will cause this too. The gaskets are side specific and can't be switched.

Don't forget where the injector goes into the intake manifold' I've found one of the "O" rings leaking vacuum there in the past.

The hose bib under throttle body, power brake booster, plenum near the fuel pressure regulator; runners to plenum, runners to intake, intake to head.

If any of the plugs are getting oil fouled, the intake gasket could be leaking from the lifter valley.

Hope this helps.

Jake

thanks Jake, i have used the propane method so far and the motor didnt behave any different.

I want to bring up the point again of my FP guage going ballistic. I mean jumping from 30-90 or so psi like crazy just flickering back and forth....can a dang vac leak do THAT much to it??

check your valve lash again.

I would check that regulator 30-90psi isnot normal.

Okay, that's exactly where I'd concentrate my efforts, on the fuel pressure regulator. I'll bet the bladder is not sealing or has a hole.

Are you sure you re-installed it in the correct order? There's a specific order the parts install.

With that much fluctuation and the horrible vacuum readings, it's got to be sucking air pretty badly.

I'e never had one act up that way at all, but all indications are that your main source of leak is right there. There may be other leak(s) as well, but start with the FPR.

Keep me posted.

Jake

ok, well quick update guys, when the car starts surging (specific to diff. temps) and i romp on it for a quick second (like powerbrake/stall it up) it will behave great and idle perfect.

Again, to clarify: i come to a light, car starts surging, i step on the brake and give the throttle a quick "blip" and then it idles well.

ALSO, i noticed it behaves much better in cooler/cold weather?? It doesnt surge as often in cool weather (like 55-60*)

in the heat its a bitch though...does it about every time

still thnik it is the regulator????

uggggggggggh

try blocking ALL of your vacuum hoses and maybe even unhook the IAC and see if the problem is still there.

Did you ever have ur chip burnt to accept then new modifications. I dont see why those problems would be causein that much of a problem. I bet that the computer just does not know whats goin on so its tryin to compensate but just not able to handle the new amounts of air/fuel. If u havent changed the chip then that is ur problem.

Jason

yes, i have a custom prom also......i am ready for a nice RPM Vortec manifold and 750 carb....and a real cam

i figure, s c r e w it.......those mods will dump me righjt in the 11.50's!!!

bahhh, but all my hard work w/ TPI keeps me from doing it at the moment :/

If you've checked everything and don't find a vacuum leak then you're going to need to use a ScanTool or Diacom to see was kind of information your IAC, TPS and MAF are revealing.

I've only had a surging experience once and it was traced to a bad IAC wire; making only intermittent contact.

Try diconnecting the MAF connector and see if the surging clears up; if it does, then that's your problem.

You can also try tapping the MAF with the handle of a screwdriver while the engine is idling. If the engine stumbles, it's the MAF too.

Is the engine going closed loop? How active is the 02 sensor; if it's lazy, that can cause a idle problem too.

Did you check for any stored error codes?

Try disconnecting the battery for 30 seconds (after checking for any stored error codes) and see if the problem continues once you reconnect the BAT.

Hope this helps.

Jake

Hey again Jake Jr

Firstly: thanks for keeping up on my threads and following up, etc...same to everyone else, it means a great deal to me!!

Secondly: I use Datamaster for my scans and TO ME the typical TPS, IAC, etc #'s look normal. Obviously they fluctuate with the surging, but still pretty normal IMO.

I am SD not MAF, but all that was good advice for a MAF car w/ my problem.

Engine DOES go into closed loop, very normally, 02's look good (fluctuate with surging obviously), but they are "active"

No error codes at all

Battery has been in and out for long perods of time so the PCM has been "reset"

Im going to have soem time to do a final "propane test" and if i cant conclude from there, hen the plenum is coming off again for a new regulator.

I just have so many bad experiences with runners and plenums LOL....cast aluminum is not my friend. Stripped threads, etc etc (i ive worked on a gazilion TPI set-ups and the stuff is made from junk :/ :shudder:

PS, if any of you will have a look at my scans from Datamaster, i would be very appreciative and can send them asap!

I would like to see the data line. It sounds like you have thought this through very well, so you may have already done this.

Check the fuel pressure with the vaccum line to the regulator disconnected. If it still fluctuates then, you know you have a fuel delivery problem.

Even though the ECM is reading good numbers in the IAC, if the IAC motor itself is not properly responding, then you will get an idle surge. A Tech 1 has the capabilites to test IAC step counts so you can verify the integrity of the IAC.

Being that it seems to be related to engine temp, you may want to inspect the ECT readings.

Just remember that the erratic vaccum readings you are seeing may be a result of the enigine surge and not a cause.

Good luck, stick with it and you will find the problem.

blown 87...good points also

you stated you would like to see the data line?? Did you mean you want to see my DataMaster run(s)?

whats your e-mail addy? I will check your profile and see if you have one there also.

Ohh, and the IAC is new also. It COULD be a "bad" new unit...it happens, but it IS new for what its worth

E-mail me the data and we'll see if anything stands out.

Well, that Speed Density part tells me a lot. That type system is known for its limited adaptability to engine modifications.

If all the checks you perform turn up nothing, I suspect you're going to have to save a trace of the data in various operating conditions:

Closed loop: idle (both in and out of gear), part throttle cruise (different throttle positions engine under load) and WOT (engine under load.)

Open loop: Stone cold start up.

Then send it to a PROM programmer for review and modification to your PROM.

Jake

It sounds like it could possibly be the timing too far advanced maybe.

new info at the bottom of original post..please have a look

Don't be concerned about the "Late Ignition Timing" indication area on the vacuum gage; it's meaningless when a performance camshaft has been installed.

A lower vacuum reading, (lower than with a stock cam) is normal too whenever you install a performance camshaft. The more radical the camshaft, the lower the reading will be.

Whatever the reading is, however, it should be stable. I take mine off the brake booster.

I'm not sure what the duration/LSA specs are on the new camshaft you installed, but based on the 269 number in your sig, 750 RPM should be high enough for the engine to idle well, IF the idle is holding relatively steady and you have no vacuum leak.

If your idle is not relatively steady though, the RPMs could be dropping into the 600 range which may be too low for the camshaft.

As an example, my "Desired Idle Speed" burned in the PROM is 850 RPM, Closed Loop, Idle in Park. When I monitor it using Diacom, I get a reading as low as 825 RPM and a high of 900 RPM, meaning that it's ranging over an area of 75 RPM.

I doubt if it's possible to get the RPM to remain rock steady at the "Desired RPM" setting but if you can keep it within 100 of that value you should be fine.

Hope this helps.

Jake

Hey Jake...thanks again for the insight bud.

I am not worried about the "low vacc" b/c indeed a "hi po" cam will create those lower numbers...but i am annoyed by the wacky FP still.


I'm ready to spray this car back into the mid 10's and i dont want to do it w/ this problem.....again, car runs great..but something cant be right.

Any updates, my fpr does something close to this also...