this is in a 91 RS 305TBI/700r4, only 64k on the clock.

when the engine is cold, it will run decent, small hesitation but otherwise fine, once its warm it will have a huge power loss, bucks, and has a tendincy to stall with a rough idle, i checked and adjusted the timing, to 0 degrees, which if i recall correctly should be the center of the middle tooth on the timing mark.

new plugs, wires, rotor and cap.

any ideas on this, it makes the car miserable to drive.

 

After checking for a vacuum leak first, try replacing the MAP (manifold absolute pressure) sensor. The sensor is about $30 at an auto parts store. The sensor went bad on my LT1 and was causing the same issues.

 

Another thing thatll do it is a bad CTS.

 

agreed.

 

well i swaped in the map from my 87' and drove it around and it didn't make any difference, so i'm ruleing that out.

however when i took it out tonight, it felt prety good above a certin RPM, but low rpms and from a dead stop it wants to hesitate and chug along till it passes a certin point then runs great. i'm staring to think its a fuel starveing issue, so tommrow morning i'm going to change the fuel filter and oxygen sensor and see how it feels from there. if that dosen't solve it, i'll give the CTS a try.

 

I have a similar, if not the same problem.

I went chasing a spark, but I was wrong. However, I got a whole new ignition system.

A cts would do that and its a relatively cheap fix. I changed mine and it did not do jack.

A MAF could do that as well.

Your IAC, idle air control sensor could be faulty. Basically just take it out, spray it with some carb cleaner, and see if from the start of the spring to the tip mesures 1 1/8". If its out a bit, or it seems stuck and such, than either clean or replace it. If its out a bit just push it in. Just under 1 1/8".

TPS: Sounds like there might be no problems from the TPS, throttle position sensor. Its worth checking.

Vacum leak will do this. If you are still runing a stock air cleaner, than for sure take it off and turn the engine on. Than you will know whats going on. Note, that a hiss will be coming from the TBI, which is natural, however, it should go away when warmed up and idleing.

Timing, and firing order. Its easy to get them messed up.

Fuel, and Fuel preassure regulator. So a fuel pressure gauge will help.

Start troubleshooting.

I am suspecting either a sensor or a vacum leak.

Try new 02 sensor.

Good luck.

 

O2 sensor....

 

Did you know that, you are probably running rich when you're chugging along in the low RPM>


I have the exact same problem.

I replaced the CTS
Cleaned IAC
Changed the whole ignitions system
Now I am changing the map, and o2 sensor and seeing how they do!

It shouldn't be a fuel thing, since you are getting enough fuel when you get over certain RPM. But a new adjustable fuel preassure regulator.

I let you know what happens, and you let me know what you did/

Laters.

 

Another guess is TOO much timing. When I had the 305 heads on my 355 with TBI, mine would surge on the highway at 70 going up hills in OD. I also had a rough idle with the A/C on and the engine heat soaked. Further I had a little stumble at TIP IN. I just about went crazy trying to find out what was wrong. Everyone had been saying that 6* advance gave more power so I had my timing set there. Moved the timing from 6* back to 0* and the surge went away.

 

well i changed the fuel filter this morning, that alone helped the car alot, but regaurdless i'm still stuck with the low rpm bucking and what feels like a misfire untill it picks up to about 10mph.

from a dead stop the car will sorta chug and not have much power till about 5-10mph then it will take off like it ought to and as long as i'm cruiseing around it will be fine. i double checked teh rotor, it looks ok.

as for the timing, i just retimed it yesterday, to 0 degrees. i'll probably double check it before the days out.