85 Still Surging
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From: Glen Rock PA.
85 Still Surging
Yes its me with the same problem surgeing, so far i have drove 2 mech.nuts trying to figure this 85 out, What we have so far is all sensors are doing there thing, We put a prom out of a 88 Z28 in and the surgeing went away but didnt run the best because it wasnt made for my 85 so i ordered a new prom a stage 2 chip because i have headers, cat back , gutted cat, bigger inj, The new chip came we installed it smothed right out so we went around checked timeing, idle, every thing OK it sat there and ran 2 hours no problem so we pulled it into the garage for the night, went to take it out in the morning same problem all over again started surgeing, go figure, put the 88 prom back in and it idled like a baby, but wouldnt run for sh%t, we noticed that when its surgeing and the coolant fan comes on it stops surging ,fan goes off it surges, hot wired fan direct it still surged, also when we put the ECM in its limp mode it smothes right out,Trust me we tried everthing under the sun my only wish is that i would have put fire insurance on this thing, HELP..........
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are you getting any codes when it surges?? Mine has been doing this for a while and i have thrown everything at it i could new sensors realys you name it. I was checking my connections and bumped the MAF connector and it died. Spliced in a new connector and no more surging!! I have seen this surging thing happen a lot with these cars it could be anything from maf relays to ECT sensor or an bad wire somewhere. If you have any codes it will help you go towards the right direction.
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From: Glen Rock PA.
The prom he found in his shop was thought to be from his 88Z now i dont know 1 from the other but i do know that it did idle with out surging, and as for the maf relay thats should be mounted on the left firewall we couldnt find it if its there. all i know is that everything that is bolted on as for sensors has been checked rechecked and nothing found.have tried 3 ecm still same problem, have flooded engine with water to check for vacuumn leaks we have tried every thing but exorcism,i,m not an expert with this TPI but the fellow working on it is a very good mech like the 1 before him but this car has them stumped.Also no codes comeing up.
Last edited by 46snake; Sep 9, 2005 at 11:25 PM.
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From: Gansevoort NY
Mine is also surging. I have just begun to try to troubleshoot it. I reset base idle and as soon as I disconnect my IAC it idles fine. After resetting the idle I reconnect the IAC and its back. The TB is dirty so I am going to go that route next. Then try the reset again. After that I haev read that a couple members have had luck getting rid of it by replacing the O2 sensor which is on my list to do anyways. Lastly I have read that a weak battery has caused surging. If I find mine I'll let you know. 
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From: Glen Rock PA.
OK been there and done it new battery and sensor i,m telling you guys if it comes off its been replaced or rechecked, why does it smooth out when the fan comes on and when it goes off it wants to surge again and we jumped the fan but it still surged?Also dont understand why it smooths out with the other chip , not sure now what its out off but it smooths the engine.....
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From: NORFOLK VA.
[QUOTE=46snake]I ordered a new prom a stage 2 chip because i have headers, cat back , gutted cat, bigger inj, The new chip came we installed it smothed right out so we went around checked timeing, idle, every thing OK it sat there and ran 2 hours no problem so we pulled it into the garage for the night, went to take it out in the morning same problem all over again started surgeing.
Ok your stage 2 chip was it custom burn for your combination or was it just off the shelf if it is off the shelf then it wasnot burn to work with your larger injectors so its a possiblelity that it is to rich and the ecm is trying to ajust but cannot,what size injectors are they? When the fan comes on the ecm increases the iac steps to raise the rpm up to compensate for the small drop in rpm that happens when the fan comes on.Starting it the morning would really make it worse because you have extra fuel from the cold start injector being tossed in there too with your larger injectors
In (my opinion )you need a program for your 85. 
Ok your stage 2 chip was it custom burn for your combination or was it just off the shelf if it is off the shelf then it wasnot burn to work with your larger injectors so its a possiblelity that it is to rich and the ecm is trying to ajust but cannot,what size injectors are they? When the fan comes on the ecm increases the iac steps to raise the rpm up to compensate for the small drop in rpm that happens when the fan comes on.Starting it the morning would really make it worse because you have extra fuel from the cold start injector being tossed in there too with your larger injectors
In (my opinion )you need a program for your 85.
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Drifting
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From: GA
Originally Posted by 46snake
and as for the maf relay thats should be mounted on the left firewall we couldnt find it if its there.
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From: Glen Rock PA.
The new chip was custom burned from the same info about motor as i stated herei think it was TBICHIPS . out of NC., I'll try to find out about that other chip like i said john found it in his garage and the only chip he remebered changeing was in a 88Z he had.
Last edited by 46snake; Sep 10, 2005 at 11:19 AM.
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From: Germantown OH
How is your fuel pressure? Is it steady? The reason I ask is that I had a surge which was caused by a hole in the soft fuel line which connects the fuel pump to the hard line. As pressure in the system came close to set pressure, the fuel would spray out of the hole causing the pressure to drop. The fuel wasn't atomizing. Add in O2 sensor and ECM compensation and you get surging. At least I did. Hope this helps, good luck.
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From: Glen Rock PA.
Yes my fuel pressure was checked it was OK, like every thing was checked and rechecked or replaced this car has been in 2 garages so far all top line mech. Running out off options and $,
Last edited by 46snake; Sep 10, 2005 at 11:31 PM.
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From: Glen Rock PA.
Brian, the fellow who burnt the new chip says that the computer is not reading the prom and running off the tiny chip beside the memcal chip. But he doesnt say why or what could be wrong this is my 3 ECM so i dont think it could be that.
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From: NORFOLK VA.
Originally Posted by 46snake
Brian, the fellow who burnt the new chip says that the computer is not reading the prom and running off the tiny chip beside the memcal chip. But he doesnt say why or what could be wrong this is my 3 ECM so i dont think it could be that.
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From: Gansevoort NY
I was doing some light reading yesterday moring(85 corvette shop manual) and discovered that if the Evap canister selenoid isnt operating correctly it could cause a surging idle .I added this to my list of items to check.
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From: Glen Rock PA.
Im haveing another chip burnt ill let you know in about 6 days if thats the trick. were pretty sure that it is because when we put the chip from a 89Z in (yes it does fit) that it clears right up but wont run right after 2500RPM because its not calibrated for my 85. If thats not it make me an offer i cant refuse.... Thanks everybody Ron...........
