Good day everyone, i have a 1990 caprice with a tbi the engine is the 305 (5.0), i am having trouble with the car and i searched the whole internet and couldn't get a clear answer, the car when in idle on P or N runs great even when given gas but when i put it in drive it stutters and almost seems like its running rich, i have replaced the distributor cap with a new clean one i had laying around, and got her new ACdelco spark plugs and spark plug wires and redid my timing correctly using the timing gun but the car still didn't run correctly, i removed my injectors and cleaned them but it still didn't work any suggestions on what i should check? Thanks in advance!

 

Could be a multitude of things. Easiest, most time and cost effective starting point would be connecting an ALDL cable and running an OBD1 Scanning/tuning software like TunerPro RT. In addition, keep your timing light and evaluate fuel pressures. With these three items it should help pinpoint what needs to be addressed.

Have you pulled the trouble codes by jumping pins A & B on the ALDL with the key on? That could be a start. Even stored codes not registering the SCS light can help locate the problem(s).

Without these troubleshooting techniques you're kinda of stabbing in the dark and throwing parts at it.

Common problems are vacuum leaks - be sure to check everything really well.

 

Does it have a rough idle when cold? Or does it only start when warmed up? My TBI from cold start idles great, then once it warms up and goes into closed loop it will shake at idle in drive around 550-600rpm. If I shift into neutral or park, the rpms go up by about 100 or so and the shaking stops.

 

@bennettcvcu i once trying jumping terminals to reset the IAC valve, and i cant find an obd1 port where i live so I'm going to check the fuel pressure next its easier to do and i can borrow a fuel pressure tester. And for the vacuum lines ill leave it till the end because it a pain to do.

 

@Smykster ill shoot a video tomorrow maybe it'll help, but when cold it turns and idles good with no issues at all but when it heats up a bit it starts to idle really rough like it's surging and it stays like this until its really rough that it dies, and its worse when i put it in gear i need to keep giving it gas to keep it running

 

Verify all of this that you haven't done already:
The Usual Four:

1. Verify System Voltage.Most “12-volt” batteries should show 12.6—12.8 when fully charged, depending on battery construction and temperature. A “12-volt” battery measuring 12 volts on an accurate voltmeter is near-dead. Assure battery connections are clean and tight. Battery voltage during cranking should never go below 9.5 volts, and then only when the battery is very cold (below freezing.) Higher voltage during cranking is better. Running voltage--alternator charging--is generally 14.x volts measured at the alternator output terminal.
2. Verify fuel pressure at prime, at idle, and under load. Most fuel pressure gauge assemblies have a push-button pressure release connected to crappy vinyl tubing. Route the tubing so it empties into a drain pan, then push the button while the engine is running. This simulates higher fuel demand if you can't check fuel pressure on the highway. Fuel pressure should remain steady even with fuel flowing down the pressure-relief tubing. TBI systems don't hold pressure when the pump stops running. How old is the fuel filter? Have you ever dumped a bottle of Chevron Techron Complete Fuel System Cleaner into the gas tank? (Recommended at every oil change.) Use Top Tier fuel which has additional detergents beyond what the EPA mandates, to keep the injectors clean.
3. How old are the usual “tune-up” parts and procedures? Inspect/replace distributor cap, rotor, plug wires, spark plugs. Use quality parts sourced from an authorized seller (NO COUNTERFEIT PARTS FROM AMAZON, EBAY, OR OTHER SKETCHY SELLERS!) Be sure the ignition coil will reliably fire a spark-tester calibrated for HEI when the coil is fully warm, and misted with water from a squirt-bottle. Cranking compression test of all cylinders while the spark plugs are removed. Verify EGR, PCV, EVAP, and Heated Air Intake (if used) systems for proper operation. Verify proper initial timing and electronic spark advance. Replace old O2 sensors unless you can PROVE that they're working properly—old O2 sensors get lazy, they don't provide accurate data, but they do provide “data” that fools people into thinking they're “working”. The catalyst output temperature should be HIGHER than the inlet temperature once the engine is at full operating temperature.
4. Connect a scan tool (NOT a crappy “code reader”) and look for “codes”. More important, look at the data stream to verify EVERY sensor and computer output. Verify fuel trims and knock counts during the time that the vehicle is not running properly. “Codes” have official diagnostic procedures that will be found in the service manual set for your vehicle.