Unknown1329

Hello, I want to thank you a head of time for any help given!
My 350 is having surging engine speed problems. I have replaced the coil pickup on the distributor, cap, rotor, plug wires, and plugs (Bosch Platinum). The engine will randomly drop rpms and about stall then jump up higher than normal and back to normal. It does it while driving and at idle. It will stall at idle. It only does it sometimes more and more recently. I really need this to run right. It is a TBI. The only thing I've checked so far or know to check is the spray of gas into the throttle body. It is fine and stays normal when the rpms drop it never slows down or has an odd spray. Again any help is much appreciated. Thanks, Spencer
I took it for another drive tonight and only went a little ways because it suddenly wont go over 2000 rpm. it surged back up to around 3500 quickly then dropped again. It has never stalled on me driving once while idling. it felt like it was going to stall tnight but never did. Where i drove it was all up hill (first 2 miles from my house all up hill no downhill or flat) and didnt want to go any further and end up stuck. PLEASE I NEED HELP!!!!!!! I need this to run right it as of now is my only car and i need it.

hicksvilleshick

throttle position sensor? hard to really go much of anywhere with the lack of info...


:chug:

Unknown1329

What info do you want ill tell you all i know just ask tell me what you want.

40native

First thing I'd check is your battery cables on BOTH ends for cleanliness and good tight contact. Second thing that comes to mind is the mass air flow sensor which is actually close to the air cleaner in the intake piping.

73shark

Might check fuel pressure.

3sixty

map sensor is something to think about also. map sensor tell the ecm what the fuel air mixture should be. There are ways to test the map sensor. You can google map sensor test and get instructions on how to check it. Just a thought.

Unknown1329

A family firend stopped by to help he's been a mechanic for years. He pointed me towards the tps. I'm actually on my way right now to the auto part store to he one with him since my car isn't running.

hicksvilleshick

let us know the outcome...


:chug:

jack0723

There are many things that can cause this problem. All the above suggections are definite possibilities as well as some things like grounds (check them all!!), vacuum leaks, an exhaust leak confusing your O2 sensors. Check the ground strap between the frame and engine block. I had that one bite me in the a$$ recently. Do you have access to a scan tool? If so, what kind of readings do you get for fuel trims, temperature, integrator, O2 sensors etc..? Did this problem just suddenly appear or was it gradual?

You can also see what appears to be a normal spray pattern from the injectors, but, the injectors could need to be rebuilt / replaced. The o-ring seals do rot, especially with the new blends of gasoline we have. Ethanol wreaks havoc on the rubber. How are you checking the spray pattern? If not using a timing light, do so by connecting it as if you are going to check the ignition timing. It's been a while, but I THINK you want to connect to #3 cylinder, but in any event, you can change cylinders until you have a perfect view of the spray pattern. If your light has an adjustable advance ****, you can "fine tune" the visibility of the spray pattern by turning the advance **** (engine running and light aimed at the injectors of course). You don't want to see any drips at all from either injector. The spray pattern should look like a perfect cone. Another problem could be your Coolant Temperature Sensor to the ECM. A quick way to eliminate this sensor as a problem is to unplug it (engine off) and install a 640 ohm resistor in the wiring harness plug. This will tell the ECM the engine temprature is around 160 degrees and the engine should run fine - just a little tough - not bad - to start if it's cold.

Is your EGR stuck or sticking? This will imitate a vacuum leak, but since it's internal, you can't see or hear it. This will definetly screw up your idle, but typically if you floor it, the engine will smooth out. At a steady low RPM speed, the bucking will come back.

Last but by no means least is a plugged Cat. You can test this by removing an O2 sensor and idling / driving the truck. The hole in the exhaust from the removed sensor should be enough to allow the engine to breathe and you should notice the difference.

Again, it's tough to analyse without more information. This needs to be scanned and all inputs to the ECM checked. Your computer is trying to compensate for a problem it sees. We just need to find the problem. In any event, I hope this helps.

Good luck and please let us know what you find.

Jack

jack0723

I forgot one other possibility. Those distributors have a fairly common problem with the internal pick-up cracking. It is the ring mounted inside to the base of the distributor housing. It will have eight points pointed at the distributor shaft. If this is cracked it will cause the engine to miss, buck - basically run lousy. Sorry I don't have the correct verbage in front of me and it's been a while since I had a distributor apart, but you will see what I am talking about if you look in there. Obviously you will need to remove the cap and rotor. The ring will have wires running out of it. You can't miss it. Also check for slop in the distributor drive gear. It is softer than the Cam driving gear for the distributor, and I have seen these wear to almost paper thin.

Again, I hope this helps.

Jack