Good day everyone,
I hope someone can assist here. My 71 1800 has been having a problem. She has the original engine B20E. What is going on is, there is a HARD hesitation while driving at a steady speed/rpm. We have not been able to recreate in the shop. Seems it is only while under load (driving). It feels like a flaper or whatever in the air intake is closing off all airflow for a split second. The hole car then "bucks" hard. Has any one had this condition, and knows what to do? She runs good, and is at 248K miles. P.S. The condition goes away with a slight increase or decrease in rpms. Only happends at steady rpm under load. We have replaced the Throttle Control Switch with a new unit. I have preformed the adjust check. I count 15 clicks than a large gap (around half to 3/4 throttle) then almost full open, I get a few more clicks. This gap makes me think it would be in the area of 50-65 mph on the road, and that's the area where the bucking is hardest. Am I doing doing something wrong in the adjustment of the switch? Could it be ellswhere? This was slightly happening before I added items like the fireball elec ignition, and replaced the injectors. So I don't think that's it, but on these system, I just don't know. I was even thinking timing chain slop?

Help please.

The classic cause of this is indeed the throttle position switch. You should be able to get exactly 20 clicks from it, evenly spaced. Perhaps the new switch is defective?

pardon my neophyte ignorance...

where is the throttle position switch located?

It's on the forward end of the intake manifold, connected to the shaft the throttle butterly rotates on. Roughly rectangular thingy, about 2" x 2" and 1/2" thick.

found it. thanks

The best way to diagnose the TPS is to simply unplug it. Try pulling the connector out and driving around as normal. Unless you are doing quick throttle openings you should not even notice a difference in performance and it definitely won't hurt anything. If you cannot recreate the bucking situation after a while then you can safely assume the TPS is the culprit. If bucking does continue you will at least be able to rule it out as the problem. (been there...).

Post back with results after you try this.

good point. i would check the connector at the tps, the harness and the grounds on the intake, too. good luck, chuck.

Hey All,
Well, I've been tinkering and tinkering on that adjustment. Had to slightly backup the cable to make it just before tight. And I played more. I am now getting 23 clicks, just about evenly spaced throughout the movement. I just got back from a 40 miles run. Well, the bad pony buckin is gone. Thanks, I was getting saddle sore. Now, two things that have comeout of this. I seem to feel a decrease in power (I guess I can live with it), and there is a (how can I say it, ah..)....a quick lope and return when dropping to idle. The lope goes from 850rpm and back to 1100rpm in a second. Think maybe my mechanic, in his wonderment of the throttle switch situation, changed idle settings or something? Or is it that I just have to keep playing with the T-Switch till I get 20 clicks per movement?

Don't adjust ANY of this with throttle cable tension. The throttle cable should be completely slack when in the rest position. You're affecting both the butterfly position AND the Throttle Switch position when you do this. There are seperate, proper, and necessary adjustment points for both of these.

The Throttle Stop Adjustment Screw, to keep the Butterfly from binding in the Intake Manifold, and the Throttle Switch Mounting screws.

The best thing is to get and follow the '71 E Shop Manual instructions, in proper order. Otherwise, unless you look very, very closely, and succesfully figure out the entire system, as it was made to work and be adjusted, you'll just be chasing your tail.

gary - '72 ES, '67 122S

You might try disconnecting that vaccum line to the distributor and see if that helps maintain a steady idle. I think my distrbutor was a bit wonky, but with the retard hooked up it would only slowly settle down into a fitful idle after about 3 or 4 seconds. Then when I started to move from a dead stop the engine would just bog for about 2 or 3 seconds before coming to life again. I plugged that vacuum line, readjusted the idle, and now it drops right down to idle and takes off immediately.