ok heres my nightmare, i just bought a car with a 383, afr 195 head, zz409cam, 1.6 roller rockers, and yes the mini ram. the problem i am having is that the motor is surging at idile it jumps about 1000 rpm up and down. heres what i know about the car. the guy that i bought it from said he had originally got it tuned for the corvette l98 heads, and later upgraded to afr heads, he replaced the maf with a new one from auto z and it ran worse. i recently changed all the spark plugs and gapped them at .55. i also cleaned the iac sensor and that still didnt help.the car has 24 pound injectors on it as well. im having this problem i know its alot just want to know if anyone can give me any advise thanks

what plugs are you using? gap them tighter at like .040 or so.

MAF sensor, i'd use a GM one and none of the aftermarket stuff

But if it was tuned for the L98 heads, the AFR's are gonna change things so it sounds like it needs retuned

i just swapped out the maf with another gm one. the surging slowed down a bit at first then started up agian. also the surging only happens after about 5 or so minutes of the car being turned on. i am using autolite 3923s what the afr website called for it previously had ngk bkr5e. the car does stumble a bit when take off now like a burned spark plug wire. im going to regap them tomm and see what happens. im going to go about 50 thats what msd calls for and it does have the box installed thanks for the help

i gaped the plugs again today and it made a big differance. but i still have the surging problem. i might try a new iac valve? anyone think it might be out thanks

AFter 5 mins or so after a cold startup, it sounds like its having problems in closed loop and may need tuned.

Sounds like its too rich at idle and the stumbling off idle is another sign of too rich

well its not really a stumble when driving just when sitting at idle. today i again cleaned the iac valve and same results. i was thinking of re setting tha iac valve. is that a must when caming the tpi set up? thanks

yeah it should be reset after cleaning to be sure its right but i'm not sure that will help anything. I dont think this is a simple issue with external parts... i think its a tune issue

But disconnect IAC and start car, set idle speed to about 100 rpm lower than whatever it was tuned for in the chip. Shut off car reconnect IAC and turn power on but not start. Let it sit for 30 sec, key off then start up. Should be set properly now

The tighter plug gap hints to me that its still running rich and the tighter gap got better burn, and helped out the issue. But still needs some tuning with idle fuel.

I think we need to see some scan data on this car to pinpoint what is going on here. Do you have access to a scan tool or anyone with a laptop with any scanning software?

If you are in Arizona you could bring it by and I could do a scan on it for you?

I would like to see your MAF readings, BLM counts, IAC counts etc,

I don't think it is a timing issue but what is your timing set at? Have you double checked you are getting smooth spark on each cyclinder wire? Just something to rule out before we proceed.

thanks guys for helping out, i do belive it does need tunning because of what the guy told me after i bought the car. im going to try and reset the iac and see what happens. i wish i did live in arizona because i dont know anyone with a scan tool or anyone that could help. i appreciate though and if i do come across something i will let you guys know or i will end up carbing the car. i cant afford tunning thanks guys ps almost forgot when i try to set timming i cant advance past 10 and also the chip was burned by tpis thanks

Don't carb it. That is a nice setup. You will actually kill the value of the car if you carb it. We really need to see a data scan. Put a post in our regional board asking for help with a data scan. Trust me someone nearby to you will have a scanner or software to help. The scan is the key to the mystery.

i found some one that has one around here i just dont know when he will get around to actually scanning the car. my plan was to take the motor out and put it in another car. put a stock l98 back in from a corvette. that way i dont have to tune as much but im still in the process. thanks again but i will post something up as soon as possible

check for a vacuum leak on the intake and runners

I'm in the process of building the almost exact same engine in a 91 Z28 and have spoken with Jim at TPIS several times and he said that going to a 383 would require atleast 30lb injectors. i'm not really sure if this is your problem but I would give him a call. Also I'm sure he could help you with any tuning issues. They have a stage 5 tune for I think around $500.00 which would be a custom chip just for your car.

yeah i thought the injectors would be too small but i didnt build the car so thats where i lose. i cant really afford the 500 dollars either so i really want to just take the 383 out and put in a stock vette l98 with the mini ram think this will work on the stock chip?

If "will it work" you mean will it run. Yes it will but won't be optimum. Your best bet is to start hanging out at the DIY prom section. Otherwise buying someone's one size fits all prom will lead to disappointment. You can burn eproms for less then $500 and have a much nicer running car. Let's be honest you don't have the money to tune it but do have the money to swap out the engine and buy a mini ram?? Take a step back and find someone who will help. Or buy a cheap laptop to scan. Then buy some prom burning equipment and an eraser or the other alternatives out there. Learn how to DIY and never look back. It's not that expensive. You might end up increasing your MPG to help offset costs. Plus you'll be able to troubleshoot and understand whats going on when gremlins show up. This is just my .02. If you don't want to put forth the effort then you should have just bought a car already tuned or with a stock engine. There are plenty here who will help.

If you put a miniram on a stock L98 make sure you have the 1204 miniram. I was going to do the same thing only I have the 1205 miniram which has larger ports and was basically intended to go on aftermarket heads. I am not sure about the aluminum heads on a vette L98 but the iron heads on the Z28 L98 have a lip on them where the valve cover sits and you have to do a little grinding on the heads to get the intake to seat properly or you will run in to sealing problems. Also TPIS has some cheaper options as far as chips go, I called and give them all my information and he made a chip for my car with just the miniram but like I said I found out too late about the 1205 and the head problem. So now I'm going to change my heads and send the chip back and pay the difference. As you make more mods to your car you don't have to keep paying the full amount of chip just the difference in the stages. For example the chip I ordered was for a miniram and some bolt on's and it was $375.00. Now I'm going to change heads and cam and it will only be $125.00 more. Anyway I will let you know how it works once I get mine all together. Let me know if I can help you with anything.

I know this thread is a little old but I recently looked at his car and it really has a nice setup. I hooked up my laptop and did a WINALDL scan and I am really wondering about the camshaft.

The LSA is 112 but the MAF readings dont really match up at different points during the datalog. I am thinking that it might be that the TPIS cam is non-computer controlled or maybe the overlap is causing it to surge.

Anyhow, it looks like the chip in it is a modified 32B tune and has been worked over somewhat.

I am including a slightly formated Excel datalog from WINALDL. There are some real irregularities in the data, which I really have not seen before, but it maybe due to us hooking the power supply of the data cable directly to the battery.