My stock 1986 iroc 305 auto shakes very hard on drive when idling with the brake on. It shakes like if it was Cammed .. Also when I slowly release the brake, I can hear knocking noise underneath somewhere on the floor or firewall then it goes away as I press on the brake harder. I do my own work so I知 guessing it could be loose motor mounts or transmission. Car needs new spark plugs so I値l be doing that too. Just want to narrow my problem so I can go from there. I have attached two videos .
thanks!

 

If the vacuum hose to the power brake booster is disconnected and capped, does the symptom still occur?

 

Thank you! I値l give it a try. The car kept Turning off when I would drive it and I just changed the spark plugs and wires and it stopped shutting off but still shakes hard and now it stutters and hesitates when I give it gas with the new spark plugs change. So something is wrong with the fuel and air mixture and I already adjusted the screw and moved the tpi sensor to the .054 volts. The car is a headache because it shuts off when I put it into gear. Already replaced MAF sensor, and new iac and still have an issue. Maybe I値l have to check the o2 sensor. The car is building a lot of pressure on the gas tank and it pops the tank as it expands. When removing the gas cap there is a lot of pressure released.

 

Check VERY carefully that the #5 & #7 wires are correct.

 

I have them correct. Just checked the diagram

 

I suppose a decent place to start would be checking the fuel pressure.

Trying to diagnose an engine that's been parts-shotgunned will be challenging. Is it throwing any codes? Any abnormalities in the datalog?

 

It has the check engine light but it痴 for sure from the dual straight pipe exhaust done by the previous owner which I dislike the sound and plan on going back to stock. I just purchased a o2 sensor and I know it becomes expensive just throwing parts to it. But I really need help in learning why it痴 building all that pressure in the gas tank. The tank literally expands and you can here it pop and lots of air pressure when removing the gas cap. If life goes well, I want to LS swap it in about 4 years form now. I want to keep this 305 healthy for as long as possible. It only has 57k original miles

 

Definitely obtain all the codes the engine is throwing, and check fuel pressure. That will be the basis for further diagnosis.

 

Have you checked the egr valve hose most of the time the frail and create a air leak I had to replace all mine running under the tpi manifold just an idea

 

Thank you. I値l check the egr valve and I値l buy a scanner to look at the codes. Thanks guys!

 

Btw, how do you check fuel pressure? I have a vacuum gauge that I use to check my carburetor 454 truck. I believe it痴 for fuel too

 

Paperclip will get you the codes.

https://www.fcarusa.com/TechSupport/...-older-detroitIf your gauge goes up to 43psi, you can hook it to the schrader valve on the fuel rail. If it doesn't, you need one that does. They are rentable from auto parts stores.

 

I got the codes and it gave me 36 and 43 using the paper clip. So I guess I値l have to change the MAF relay since it痴 a brand new MAF sensor and change the knock sensor. I purchased a o2 sensor but it was only 18 bucks so I値l put it on .

 

Thank you for the fuel pressure help! I値l do that