I’m having a new issue with my 1998, I suspect it is tied to my cold start issue, but I thought I would ask anyway to be sure.

After I start the truck, back out of the driveway and put it in drive I get noticeable hesitation and “fish nibbling” when I start to accelerate and it doesn’t seem to smooth out until I hit about 25-30 miles per hour or so. After the truck has been running for awhile and the engine has warmed up it runs fine at all speeds, zero hesitation or “fish nibbling.”

I have noticed the problem seems worse on damp days, the wetter it is, the worse the problem, it was thunderstorms all yesterday afternoon and night so today (surprised it even started) the problem was so bad it actually felt like it was getting ready to stall.

I assume the problem is related to my wet weather cold start issue, but why is it only a problem at low speeds? Am I correct in my assumption?

 

Until I read about the correlation of the symptoms with the rain I wondered if it was a torque converter problem or low trans fluid problem. I might be worth checking the fluid level anyway.

 

You could be right actually, I know I have a slow leak from the transfer case, I was actually planning on checking the levels again this weekend, I’m just thrown by how it smooths out when it warms up (and dries out).

 

Dirty mass air flow sensor. Clean it with the special spray. Take it a part and use a qtip to clean off all contaminants.

 

It was worse today, it was also actively raining. It was EXTREMELY rough with lots of fish nibbling and hesitation and didn’t want to go over about 10-15 miles an hour for about a quarter mile, then there was a popping sound followed by a surge in speed of about 5-10 miles an hour. Then a low grinding sound as it accelerated normally. At the stop sign the same thing happened as I started to move again, but less severe. Same thing again at the traffic light, but even less severe. By the time I went about 2-3 miles the truck was behaving normally, however shortly after the first traffic light the service engine soon light came on. A couple miles later I went to Advance Auto and had them pull the code, the code was for a random cylinder misfire. By the time I left Advance Auto the code had cleared though.

 

You know, reading this description made me think you could have a cracked distributor cap or some other fault with the wiring or insulation in the ignition wiring. Perhaps the moisture is causing shorts in high-voltage parts of the circuit by making it easier for the spark to jump to part of the engine or body instead of jumping the gap at the spark plug. I'd check the cap, rotor (since you are already have the cap off), the coil, the wire from the coil to the cap, and the wires from the cap to the spark plugs. I've also seen where sparks would jump from bad wires to an exhaust manifold. This was seen with the hood open and at night with no under-hood light on so that any sparks could be seen. With the moisture you might not see any sparks but the by-passing of the spark-plugs could be the fundamental issue.

It is not quite the same but a long time ago I had noticed that in my 68 Mustang that I could cruise at 60-65 mph but if I accelerated to pass someone the engine would cut out until I slowed down a bit and then it would start again. What I worked out was that the aftermarket coil I had installed had cracked and with the higher pressures in the cylinders when I accelerated made the spark gap harder to jump, the high-voltage would find an easier path to ground through the cracked plastic casing of the coil.

 

There are many potential causes for a hesitation. Basically an engine needs:

Proper air/exhaust
Proper fuel
Proper ignition
Proper sensor and computer function

A select list of potential malfunctions/components:

MAF sensor
MAP sensor
Engine temp sensor
Fuel pump/filter/regulator/injectors/lines
Ignition module/coil/distributor/wires/plugs
Air filter
O2 sensors
Cat
Vacuum leaks
Air intake leaks
MAP sensor
TPS
EGR
Engine computer
Voltage/wiring/connectors

Since its worst when it rains, inspect the ignition components afterwards (wet distributor, coil, etc.) Wait until its dark out then start the truck and spray water around all of the ignition chain and look for arching or listen for engine RPM changes.

Above test with the vacuum lines.

What is the complete code history? Is there any freeze frame data during an event?

Have you cataloged the combined fuel trims (LT+ST, each bank, idle and 2500rpm)?

Is this the same truck with a cat problem? Has that been resolved? Whats the back pressure?

What has been repaired/replaced before this started?

George

 

Totally right, it seems the OP has NOT addressed the BASICS of a well maintained engine, Chevy or Ford or whatever.

 

Yes, same truck, and no, I will not have the funds to do the catalytic converter until next month. This Month is the plugs wires and coil to try and fix the cold start problem.

Previous to this I have replaced the distributor cap and rotor, the air filter, the PVC Valve, the ball joints, and refilled/repaired the front differential, the front brake pads and rotors, repaired a blown power steering hose, replaced the 4 wheel drive vacuum switch, replaced the blower motor control unit, replaced the battery and battery tray, and replaced the vacuum canister vacuum line. There is more too but I can’t imagine any of it making noise or effecting the engine or driving.

Only code history I know of is the stuff for the catalytic converter and this.

No idea how to do that other thing or even what it is.

 

For what it matters, car maintenance is NOT cheap, be it a Chevy or an Audi.

Be grateful you have Chevy, my Son has an Audi, why, God only knows, but that bastard is VERY expensive to maintain.