Quote: Originally posted by BadIroc see my cam isnt that big enough to throw the idle off that bad, but im still gonna throw in the "it needs a custom prom" theory in the bin of suggestions as well Ah man, my cam is 224* @ .500" with .465" lift. It is almost identical to yours. I just checked out your webpage. Sweet car BTW.

thanks.....ya im jus gonna get the prom for it, then when i get into the heads and cam on my motor then im gonna get it retuned, dyno tuned, then any bugs that need to be worked from there then get it retuned. The guy that im gonna go through to burn my prom does buisness with the local dyno shop in my area so it works out well...

I'm going to say that I personally suspect the idling problem is due to the prom chip. Although the lift on that cam isn't radical by any means, there's a fair bit of duration there. That's what gives most engines, particularly automatics, idling problems. Also, what's the Lobe Separation Angle? The lower the angle number, the more radical the cam will behave I believe.

I can't say as far as Chevies having a history of cam idling problems, but us Ford guys deal with them all the time. The problem lies in the factory IAC valve's inability to allow ENOUGH air into the motor during idle....so the car will begin to surge. I have a 302 with an E-303 cam (220/220 duration, .498/.498 lift, 110 lsa) and it develops nasty surges occasionally. In my experience though, the surging becomes gradually worse and more radical until it results in a hard stall.

As far as overcoming surging...I will rev it once or twice then give it steady gas pedal to keep the idle around 1500...then VERY slowly back it off until the engine goes back into idle---sometimes this will put the engine back into a normal idling pattern. Upping the idle speed by a few hundred rpms will *typically* get rid of surging problems also... I've also noticed that sometimes, even adding an extra 1 or 2 psi of fuel pressure can smooth things out, even if it *does* make you run a tad rich.

Hope any of that helps.

yeah i already raised the idle speed in my car jus a tab and it seemsed to help a little bit but not much....my cam doesn't have that radiacal of lift and a 114lsa keeps it computer friendly, but has a decent amount of duration 222/226 @.050 and 267/278 adv.

im suspecting its the prom, cause right now the prom is stock for a 350 car...and i have a jet stage2 piggy back on it which does absolutly nothing, but the people that iam going to get my prom through burns piggy backs for the stock chip, just at your exact specs and the dyno shop in my area works with them as well to dyno tune then send the info out to that chip company and they burn a chip to those exact specs as well, but i wont be dynoing it again till I do another set of heads and a diffrent cam.

I will also try advancing my timing a bit and lowering my psi a bit cause as for right now iam running very rich as it is.

But i know me and many others have been strugling with this problem for awhile now and im destined to figure out this problem so I will be like I have been updating this thread daily.

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I have been fighting this problem with a few other members for a while now. I have:

compresion checked the cylinders
notched and adjusted two different tps sensors
adjusted the timing
checked the temp sensor
bleed air out of cooling system
adjusted fuel pressure
checked for vacuum leaks with carb cleaner and map gas
data loged runs
scanned car millions of times
replaced distributor
replaced map sensor
cleaned iac and passage
replaced o2s

and still have a surge!

The car surges the second that it hits closed loop. and what I have found from putting a wide band o2 on the car is that it is bouncing lean in closed loop causing the surge.

Now the only thing that comes on line in closed loop is the o2s, which seem to be tring to compensate for somthing and causing the surge. And where it gets interesting is that if I unplug my o2s and run the car in open loop all the time it runs great. In open loop all the sensors are on line and working except the o2s (speed density mode) so they must be ok for the car to run good. Where I get confused is if everything is fine what are the o2s trying to adjust for when the come online in closed loop?

My computer has been tuned by pcmforless multiple times and I am leaning tords the closed loop tune even though they say no. They keep telling me that it is a sensor. Or maybe a mass air flow that is bad but not throwing a code and has a steady linear reading when scanned.

If the computer thinks you're rich...assuming you're modified and chipped, you probably *ARE* on the rich side, it WILL attempt to trim the fuel off. But why it would bounce the trim back and forth I'm not sure about. What do your short and long term fuel trims look like?

Have you checked the EGR system? Maybe when the computer enables the EGR flow (which is at idle and maybe decel IIRC), it's leaning the a/f enough to cause your problems. If it hasn't been done already you could try disabling the EGR function on the chip and see if it makes a difference...or on an electronic egr valve I believe you can just disconnect it.
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Also I forgot to mention, check the mass air voltage at varying steady rpms...I'm sure someone has a table somewhere that will correlate that voltage you should have at X rpm and barometric pressure....verify that's correct, and then give it the stab test. From an idle with the scanner on, firewall the throttle for only a second, just enough to get the revs up to say 3 or 4k...look for an appropriate change in voltage that corresponds properly.

The EGRF has been removed and deleted out of the computer and I get a value of zero on the scanner. My BLMs are right where they should be at 128 or a little lower. The mass air readings are fine on the scanner and does not throw a code. And yes my car is tuned and runs rich ,according to my wide band around 12. When the car hit closed loop the only thing that I can see on the scanner is the O2s bouncing causing the car to lean out, this is varified on my wide band.

Where I am confused is if it runs fine off all the sensors in open loop except the O2s, what are the O2s compinsating for. I know its running rich but shouldnt that be programed in to the computer? Also is the mass air doing anything in open loop?

So this thread is dead - did you find the problem? Could you enlighten us?

Any update.........I have the same problem????

Looks like the answer is biting the bullet and taking it to the dealership and letting them plug it in and retune it......yay..unfortunately they charge an arm and a leg...

I just fixed my surging problem . Cost about 37 cents . It was that stupid little 1 inch long tube in the gas tank that is between the fuel pump and the gas line . Mine had a slit in it . Went ahead and replaced the fuel pump while I was at it of course , but the problem was low fuel pressure due to that slit in that 1 inch rubber hose .I didn't read this whole article because it was long ,I just saw the first symptons ,so if I'm off base here sorry . Just trying to be helpful .

Dang, this thread looks long gone. I have the exact redlight once car is warmed up problem. My car actualy jumps forward then almost stalls, but the picks it back up and idles down, and like you said, does it again, and again until you finally take off and it runs normal while driving. Mine also spits and misses at WOT up top.

I was the part on checking the IAC. My car is a TBI 350. When you unplug the IAC and whatnot, where do I adjust the idle?

I had this problem a few years back, and the fix was stupidly simple.

Clean your throttle body. That's it. Pull off the black plastic connected to it (at least for the v6), and just spray half a can of cleaner into it. You'll see a TON of black stuff just start pouring out.

The end. After doing this, I have NEVER had the surging problem again.

I just had this problem changed tps,iac then change temp sensor and it fixed it.

I had this problem on 2 cars, one was worse than the other. The solution was new injectors!

I welded a bung in the other side exhaust to put an O2 sensor in there, that side would surge, the other wouldn't. Checked spark plugs and 1 didn't look too good compared to the others. That injector was bad and spraying erratically, causing a misfire picked up by the O2 sensor causing a violent rich/lean oscillation. add worn spark plugs and maybe wires to the issue and you have a problem.

Had this horrible problem as well. I just got mine fixed, found out my rear intake manifold gasket had blown out a quarter inch wide. I was pulling vacumn from that.

Gotta keep the dead thread alive!!! Any other fixes care to chime in ? TBI 305 here with random surges, once in a while it dies, even on start up a few second later down to like 200 rpm then back to 700 for a few mins and every time trows a SES code

Got a question.....when there is talk of temp sensor, which one are you talking about. There are coolant temp, air charge temp and air cleaner temp sensors. My problem seems to be temperature related and it surges (looses power but does not die) more when it warms up than it does when it is cold (runs good when cold). The engine temp does seem to rise quickly. I have checked the coolant level and the thermostat. It seems like it started or had gotten worse when I overheated one time in the Summer.

there is the coolant temp sensor which is located above the water neck on the manifold, this sends signal to the ecm of what temp the coolant is, the coolant temp gauge is a green wire on the drivers side head, between the first two plugs, this sends info to the gauge. There is fan switch sensor on the passenger side of the block, toward the back, its one wire as well, think it was white, cant recall. Sometimes the piggy back on these rots and falls off, check it out from the bottom make sure its in there. There is a air inlet sensor on the air cleaner as well.

On a 305 TBI......Ok, I replaced the Coolant Temp Sensor and the thermostat just to make sure the engine was running cooler and wouldn't attempt to overheat. I also cleaned the throttle body and injectors with carb cleaner. Of coarse the engine was cool so it started fine and idled fine and ran fine but after driving it for awhile and then shutting off the car and waiting about 10-15 minutes and starting the car back up the surging and rough idle had started again. It rough idled and bogged at acceleration and smelled of gas for several seconds and then smoothed out and ran fine again. It never dies.

So the CTS and thermostat was not the fix. I guess the next thing would be a O2 sensor, which I read is a PITA to replace.