99 Tahoe Idles Smooth in Park - Rough Acceleration/Idle in Drive

[Cappie86]

My 99 Tahoe 240k miles, idles smooth in park, has rough acceleration and idle while in drive. We've replaced the plugs, wires, cap, rotor, no change. Plugs were all even colored, none darker than the other. Thinking the injector spider, MAF or both. Taking it to see what codes it's setting tomorrow, hopefully to get a decent answer and not the runaround. Any thoughts or ideas?

[Stealthee]

Rather than take it somewhere to see what codes it is throwing why don't you buy a cheap code reader? They even sell dongles that plug in and read via bluetooth to your phone with an app. You can get a regular code reader off Amazon or ebay for $15. Then you'd have the ability to run your own codes and not worry about getting a runaround.

[Cappie86]

Since my first post, we've changed the ignition coil, cleaned the MAF....still no change. The code setting is P0300 Random/Multiple Cylinder Misfire Detected. Should I look in the direction of fuel filter or spider injectors.... Once again, I'm at a loss. This old lady would love some guidance Thanks for the help!

[maxwedge]

Check the fuel pressure. You need about 62 psi key on engine off.

[bcopeland]

Change your gas cap

[Cappie86]

Thank you. I'll try the gas cap, can't hurt and I've tried almost everything else except having the injection spider changed out.

[maxwedge]

bcopeland, curious to hear how changing the gas cap affects multiple misfire codes.

[Cappie86]

Well folks... after replacing spark plugs, wires, cap, rotor, MAF sensor, coil, fuel filter, air filter my 99 Tahoe still ran badly. Most recently, it would start and stall roughly 30 seconds later. Not being a mechanic, I thought of the fuel pump. Not too expensive and a friend replaced it. So now I have all these new parts in the Tahoe and still would not stay running. We disconnected the MAF sensor and that seemed to do the trick, however, having just replaced it seemed a little odd. So we put the old one back in, connected it and still had issues of misfire, you really couldn't tell at an idle, but when putting a load on the motor it was obvious something was wrong. A 2nd set of eyes looking under the hood at the time the truck was in idle saw a spark jumping from cylinder #3, come to find out, the ex-employee who installed the spark plugs got the extension wedged between the block and steering shaft so that when he pulled the socket extension off, it cracked the porcelin on the plug. Moral of the story, be careful when installing plugs, there will probably be one that is going to give you issues, we found this to be the case when we replaced the #3 plug after we noticed the arcing. Now, the Tahoe is running like a charm (knock-on-wood)... Just wanted to post a follow up and thank you all for your suggestions!