Idles fine. Labors when you increase throttle.

I would check the voltage on the throttle portion sensor with the engine off from idle to wide open throttle.If there are any dead spots, replace the sensor. If the tps checks out, you should check fuel pressure. If you have good fuel pressure, you may want to make sure there isn't a lot of slack in your timing chain. I don't believe you mentioned the mileage of your vehicle. Best of luck.

Do you have a place where they can check the engine for contamination? Mine had a similar problem it would die after slowing down at the junction, Ask your mechanic to clean the engine and also check the throttle sensor and it will be good as new.

Good luck

I had issue similar and the end of tailpipe was missing and causing the fumes to come up inside the rear bumper and circulate into the car.

Could be a dirty throttle body or faulty idle air control valve.
Is the check engine light on ?

{: ) DTC P0506 Idle Speed Low
The usual cause is an excessive carbon build-up on the throttle body. If this is the case, I suggest you have your throttle body cleaned and perform an idle relearn procedure using a GM scan tool. The idle relearn or reset procedure is very important, otherwise this code may still remain even after a throttle body clean.
In a similar fashion, if the ECM/PCM (engine control module) of a high mileage vehicle is replaced and/or reprogrammed without performing the Throttle/Idle Learn procedure, the ECM/PCM may no longer compensate for existing carbon build up in the throttle body, causing it to return with a similar concern as well as DTCs P0121, P0506, and/or P0507.
There are other conditions that can also affect or reduce idle speed by increasing engine load like incorrect torque converter clutch (TCC) operation, accessories that require additional torque to operate, restricted exhaust, and mechanical conditions that limit engine speed.

possible fuel pressure regulator leaking high pressure fuel into attached vacuum hose

hi if your backfiring your timing is a little out also increase you idle speed on your carb by ajusting your throttle screw hope this helps if you find this useful please rate it thanks

1. Inspect the 2 wire harness for the 7x Crankshaft Position (CKP) sensor in the rear of the block.

2. Wiggle tug test the harness and inspect the harness for being melted from the exhaust manifold. Tests/Procedures: 1. Verify fuel pressure climbs to over 40 PSI during cranking and reads about 35-40 PSI at idle. Potential Causes: Insufficient Fuel Pressure
Tech Tips: The Powertrain Control Module (PCM) will idle the engine at a normal speed when the Throttle Position Sensor (TPS) voltage returns to the learned base idle value. This is also called 0% throttle angle. If this throttle angle is 1% or more at idle, the PCM will assume the engine is actually off idle and raise the engine speed to prevent a deceleration stall. Note that another sensor using the same 5 volt reference as the TPS can momentarily glitch the reference voltage low. This will cause the TPS to send a lower base idle voltage to the PCM, which the PCM quickly records as the new learned base idle voltage. When the reference voltage returns to 5 volts, the base TPS signal voltage increases to it's previous value. The PCM now interprets this as being off idle. This will cause the throttle angle to increase to 1% (or more) and idle the engine at a fast speed

check timing and set idle to 650rpm

I had the same symptoms on my 1993 F-150. A friend of mine commented that he could smell gas in the exhaust. Eventually, it got to where it would start, then die after a few minutes and wouldn't restart after that (at least for several hours). It turned out to be a bad fuel pressure regulator that was causing it to flood. It was about a $25 part and an hour labor to replace (not difficult, just awkward getting to the hex head bolts).