Rough on cold start?

[Axent]

Hi everyone,
I'm new to the forum and looking for a bit of help. Last week I purchased a 99 Tahoe 4x4 with approx. 180,000 miles on it. Right now, I'm using it as my daily driver, and am very happy with it so far. I picked the Tahoe up knowing that there were some issues with it. The seller was very honest with me and showed me everything (and so far he is 100% correct) that it needed.

At this point, I've replaced the O2 sensors, the radiator, and the fan clutch.

My question is this, the seller mentioned that it runs rough on cold start. Once it gets warm, it smooths out. And he's right.

Here's the scenario. Start it up in the morning and it runs very rough, it will even attempt to stall, it feels like it's misfiring, once I'm about 10 minutes down the road, (engine warms up) it will level out and run like a brand new truck.

Any thoughts? I haven't done a tune up on it yet, planning that for tomorrow after work, I'd just like to get an idea what else I might check for before I run up to the Auto Parts store.

Thank in Advance.

 

[gpracer1]

I would love to see what the ECT engine coolant temp sensor is reading.....not the gauge.... when it is cold.

It could be a lot of things, crusty plugs, low fuel pressure when cold, too rich when cold due to bad ECT (reading high), IAC, etc.

That is one of those times I would put a scan tool on it to read the gauges when you start it up and it is stalling out.

Is it only at ilde or trying to stall while driving with foot on gas pedal. If at idle, could be the IAC Idle Air Control motor.

 

[SunlitComet]

You will want to replace your injection spider if it has not be done already.

 

[Axent]

Thanks for the responses. I just went up to get the tune up kit. Rotor, cap, wires, plugs. I had them give me the codes while I was there. 300, 420, 430.

I didn't have them print them out, so I'll have to look them up.

300 is multiple misfires. Fingers crossed it's just bad plugs and wires, but I'll definitely look at the injector spider next.

420 and 430 are low efficiency on Bank 1 and 2 form what his ODB says. So it looks like I'll be getting a new Catalytic converter.

 

[Axent]

So I changed all 8 plugs. I didn't have the chance to change the wires, rotor and cap yet. I'll do that tomorrow. But the new plugs made no difference. Good thing is, the old plugs didn't look to bad once pulled.

 

[SunlitComet]

Thanks for the responses. I just went up to get the tune up kit. Rotor, cap, wires, plugs. I had them give me the codes while I was there. 300, 420, 430.

I didn't have them print them out, so I'll have to look them up.

300 is multiple misfires. Fingers crossed it's just bad plugs and wires, but I'll definitely look at the injector spider next.

420 and 430 are low efficiency on Bank 1 and 2 form what his ODB says. So it looks like I'll be getting a new Catalytic converter.

If you have a lack of power then chances are your cats are clogged they can cause misfires too.

 

[Axent]

Ok. So I spent the day with my new tahoe. It's actually a nice vehicle to work on, unfortunately I"m a little "under-height" so I have to practically lay across the engine to reach the distributor cap.

So here's what I did today.

1. Changed disty and rotor.
2. Changed plug wires.
3. Seafoam (Tank, Crank, and PCV)- (figured I'd give it a try). It does seem like it helped a bit. The truck is more responsive. The truck idles very nicely. But it's still kinda lurching when I'm doing 70mph. If I'm doing 80mph, it seems to run smoother, but at 70 it's not a comfortable ride. It's not real bad, I doubt a passenger would be able to feel it, but I can.
4. Cleaned the EGR Valve (Thanks to the forum Tech section)

Here's where I'm leaning. Ignition Coils? Catalytic Converter, Spider Injectors. Does anybody have any input for a novice to try to diagnose these? I don't want to replace parts without diagnosis. It's a little ******* the wallet.

 

[McFizzl]

Sucks that this thread kinda stopped. I have the 70mph jerk thing too...Idk what it is...I will see if it was my throttle cable slack. Be nice to hear if it ever got fixed and what it was.