KED85

If ya read my other thread about the Tip of the Hat to Tom P, I also mentioned how my car had an extreme case of bucking motions, as one accelerated under partial throttle. Yet if ya floored the car, the problem went away (so did gas milage!).
I went to a friend who has this great Snap On code scanner & it can read everything about our MPFI rides as one drives the car. This tool plugs into the ALDL. We checked all the sensors for anything to help with the bucking problem (and I ain't kidding, it really was bucking!).
ALL sensors checked out ok, it was narrowed down to my hokey air inlet setup that was allowing air into the engine after the MAS & causing bad readings to cause system to go in & out of alot of air, then no air.
Suggested was change back to the original air inlet set for Firebird & problem will disappear.
I tried that, and for one day, the problem was gone.
Next day, the bucking problem problem reappeared.
In that evenings mail was my latest issue of Chevy High Performance and an article about the EGR & how it can cause a hesitation in acceleration. To test the theory of the article, I was to plug off the EGR, go for drive. I took a 10 mile drive & stll had the bucking problem. As I awaited the contractor to visit the house, I looked.
I brushed against the EGR area and a hose detatched itself from "something". Scoping out more, I discovered a sensor, connected to the Vacuum Regulator Valve (which is connected to the EGR assembly in 1985 cars). This sensor is called the Vacuum Switch where this hose was to be attached. I made a great seal of the hoses and eventually took a drive home.
CAR WAS SMOOTH AS BUTTER!!
IT RAN FLAWLESSLY!
Problem solved by seeking out a higher source & keeping eyes open for ANY VACUUM LEAKS on these MPFI rides of ours.
Hope this helps others.
PS I will be making another less hokey air inlet tube from the MAS to the throttle body, as why not remove any other air leaks after the MAS.
Now I discovered that my CC rattles. Time to pull out the 1995 3.4 "Y" pipe with factory issued CC to see if it fits easily to the 1985 car.

1986CamaroSC

it's sweet that you have it fixed, must have been really annoying..

and do you have Any pic of your car?? i dont think i have seen it before

E-Z Rollin

Don't know if you saw my post in the tbi sect. but I was inquring about swapping a 2.8 mpfi onto a camaro/firebird 3.4 engine. I saw your tech article,which I read. So I take it that now everything is working o.k; did you use the computer from the 2.8 or 3.4 [overlook my ignorance of electro. terms,I'm still learning]. Do you have any pic's ?

KED85

Isn't my tech thread available anymore?
I spell out almost every detail for anyone wanting to install a 3.4 under the 2.8 stuff.
I'm almost done with the 3.4 in the Blazer, a carb version.
Yeah this bucking problem drove me up a wall.
So much, I seeked out a higher answer from another.
I removed he hokey air set up for eliminating any other air inlet air leaks. Now I will have a section made or I'll make a better air setup. I only need connect the MAS to the 90* bend I scored at a swap meet (you see that item used in this pic, supplied).
Right now, car runs, strong, but as stated, new CC is coming

Project: 85 2.8 bird

that y-pipe is gonna need to be modified, it goes straight back, into the subframe , where as the 2.8 T-pipe does that around the corner thing

KED85

I'm gonna find some solution.
Just gotta find a spare 1985 V6 manifold to cc Y pipe

Joe_L

That is good that you found the problem Ked. I know I have been sitting here wondering what if could be. Now We know.
I know what line your talking about, that little square vaccum box sensor thing. When I had my firebird, I noticed that vaccum line was missing, so I just put a new piece on, but that was before I drove it on the road, so my car could have bucked too, but because I replaced it before I drove it I never noticed.

KED85

My Wife whom drove the car, now says it started again but then stopped.
I think it's BS & she just wants me to get her a minivan sooner than she dreams.
I got tickets for the April 29 taping of "The Price Is Right", so who knows!
IF I tell everyone to watch me when I win a vehcile, believe me when I say I'm not kidding!
Actually I drive the car for about 25-30 miles tomorrow, so I'll know then.

KED85

My Wife whom drove the car, now says it started again but then stopped. I think it's BS

Well my Wife was right!
The bucking reappeared!
I went to the higher source.
I learned how to clear the computer & make it relearn the idle settings.
Tomorrow I change the EGR with another I have already, to hopefully eliminate this problem forever.
What it is coming down to is a weakened EGR spring inside the EGR assembly.

85SportCoupeto89RS

The work never ends. So many times I've fixed something just to have it come back again Drives me crazy sometimes.

KED85

That is exactly why I went to the higher source.
So far cost is gas plus two 12 pack of Corona beers!
Tomorrow AM, I swap in other EGR and drive to test (ceck SES light) & then go to the scanner for secure answer.
I'm learing alot!
Flip this...
The fix is cheap & I don't have to buy a minivan yet.
BUT, going thru an alley, I heard the brake pad squeek (break sensor!). Weds. I get to do front brakes pads (free lifetime warranty-Raybestos) & hoses & fluid.
I hope I find all my brake line wrenches in time!
It's acceptable, not thrilling, but cheap fix for keeping Wife quiet!
Plus her & Son are safer, that's good trade off!
Tired of being a mechanic!

KED85

I switched to the other EGR valve and drove in the chilly SoCal AM and still had the bucking.
Wasn't as severe as before and the bucking stopped alot quicker than before.
If this continues, I'll be buying a new GM issued EGR.
The spring in the EGR isn't strong enough, anymore, to hold the EGR closed during morning/cold driving.
Yet, EGR operates perfectly when engine has warmed up.
My car sits at idle, in gear, alot smoother, now.
Got the free brake pads and having so much fun with the hoses. Of course one side was easy. The other side, rests over night, being soaked with WD-40 to loosen the fitting. Luckily I have brake wrenches in metric & SAE sizes. I refuse to break out the Vise-Grips