Surging/stuttering idle and misfire and stalling FIX

Evilcowboy420

New member
Joined
May 20, 2013
Messages
160
Reaction score
0
Points
0
Well I figured I would post my fix for this as well as what I found out through working on my 88.

First never rebuild one of these TBI units without first buying a new IAC valve. You can take off the IAC and clean it all you want and test it for voltage all you want but it will still be bad. They were shit back then and you need a new one.

Well after doing my TBI rebuild the car kept having a surging idle and everything checked out ok as far as tests go but it was still running with a rough idle. Due to the rough idle getting worse the idle base screw had to be turned up a bit to compensate for all the stalling it was doing. Well due to the non adjustable TPS this changes the voltage and causes the computer to go into clear flood mode because it is detecting like your gassing it to start it.

I have 4 used spare IAC valves and all appeared to be working but what I came to the conclusion of is that these IAC valves from 88 to 91 were junk and once it extends to a point it will no longer retract no matter how clean it is. The only fix was to purchase a brand new one. So that is the fix for the stalling stuttering.


Now comes the fun stuff I found out. It appears GM stuck these guys on quite a few cars. Particularly the TBI 700. And apparently the throttle bore of the ones from 90 to 91 grand ams were larger than the ones on these. They also have an updated vacuum assembly with a longer port for the MAP sensor. THE FPR is smaller in size but works just fine. Well at first I thought I would have to have the intake manifold machined to accept the TBI but upon closer inspection they only changed the Bore size and not the base size so it is a perfect fit.

I ended up using a new TBI from the grand Am simply because I wanted to see if it would work and if it helped with power having a slightly larger bore. It does not seem to give it any more power than it already had but what it did do was increase throttle response and you can be a little lighter on the pedal. It also seemed better made for the grand ams since my original had some rough machine surfaces.

Also if anyone ever does the TBI rebuild a word to the wise is GM used indian head or aviation glue (more likely) on the fuel metering body to throttle body gasket. But what I have found is that gasket rarely fails.

So now there is no more stalling, no more missing and no more unpredictable idle and throttle is smooth as can be.

Now I will probably be getting a new fuel pump just for the sake of it's the last thing before the entire fuel system is new.

Things I did in the past few moths is oil pan gasket, painted air cleaner housing to a matte black, a few minor clamps, new vacuum lines, new ignition coil, ICM, Rotor and cap, and new winter wipers. I had replaced the ignition system trying to chase the stalling and surging idle around.

I also made a ALDL cable to connect my computer to the car. I used this circuit

http://www.techedge.com.au/vehicle/aldl8192/8192hw.htm

but I used a MAX232ACPE chip with a different pinout so I created a new circuit off of that design adding a led to signal when the cable gets power. If anyone wants a copy of my circuit let me know I will post it with a parts list. It's pretty interesting watching you car on your computer. Oh and yes it worked :D
 
Welcome Back EC, I bet its too cold to be working on cars up there in NY, ( thats what my sister said last night)

Glad you figured it all out, thats a neat laptop thing you made there ,simular to one on this Fiero post here?

http://www.pontiacforum.com/pontiac/showthread.php?t=31627 ( bottom reply)

I was think about getting one from him, Did yours turn out cheaper?

Doug in P.R.:cool:
 
Thanks doug

Yep cold as hell to be working on cars up here. I tend to just bundle up and work anyways. lol

Yeah mine turned out way cheaper considering Maxim Integrated gives samples out for free of the chip. I picked the MAX232ACPE cause it was a newer chip. You just have to have an email without a public domain ie, hotmail, gmail etc. I used a college email. but then again we are talking about a 0.9 cent chip lol.

The caps and resistors are merely a couple of bucks and the 5v regulator was $1.49 at R-shack.

I can get a pic of the updated design I sketched out for the newer chip since the pinouts are different.
 
Back
Top