Aloha,
I am a new member first post. I have a ZR2 4x4 that has a throttle bounce after warm on a restart. It's also throwing both banks lean. This code pops up after 40-80miles of driving sometimes 120. It runs great no issues, great mileage, no misfires nothing. The list of parts changed is long. The maf, map, Iac, vapor purge canister, pvc,
and tube all Ac Delco parts. New intake manifold gaskets and all seals changed in upper plenem. 2 new upstream O2 sensors Bosh. The only part I needed in a pinch was parts store brand TPS. I only changed it because it made sense on the throttle bounce. Found multiple vac leaks and changed the hoses. Ordered a new air box to maf seal waiting on that. The fuel pressure checked out in specs. This bounce has me chasing my tail. I still feel like I'm chasing a vacuum leak!!! The vac lines to the t case have not been changed. It ran like crap before changing out all the parts but no misfires. Every part I changed was failing, worn out or darn close. I hope someone has the ahh Bro it's this. I appreciate everyone's time. Mahalo ,🤙

 

How well does your HVAC operate? Meaning does it change air delivery modes as it should (feet, bi-level, vents, defrost)? Do all the modes work, promptly, sluggishly or not at all? Also is the surging only at idle after you first start and goes away within a mile or so of driving?

 

Hvac seems to be fine all modes work. The surge is after it's been warmed up, driven parked and restarted. No issues while driving no surging at all. It's always after idling down to 550-525. It also seems to bounce more in reverse. It's also more prone to bouncing if I fire it up and throw it in gear right away. I know it's not a tranny issue. Drivability is fine after driving but stopped at a light too long and it just seems like it wants a higher idle while in gear.

 

Also thank you Rockp2 for taking the time. 🤙

 

That idle is lower than desired. Should be ~650 RPM. What were your fuel pressures KOEO and after 10 minutes? See below my signature block for "HOW TO:" link from Captain Hook on fuel pressure leakdown test.

 

if I remember correctly I was a little over 50 on koeo. Did not think of doing a leak down test.

 

A little over 50psi KOEO is a little to low. I'd recommend doing the fuel pressure and leakdown test as the link describes and recording the exact numbers. Especially with the symptoms and all the work you've already done.

 

I Will update you on Wednesday after I get the readings. I really appreciate the information and time Rockp2.

 

Alright Rock!! I have been reading and reading on my issues and it was still screaming vac leak to me. So I went out popped the hood and started listening and looking. I found the vac leak around the vac canister. I had already changed all the hoses with a brand new and one had had a leak. I switched it to silicone and took it for a drive. All pending codes are clear and milage is way up 25 ish at 55. The throttle bounce is gone and the idle seems to up a little. I'm going to order a new Delphi fuel pump as preventative maintenance. It has 190k on the rig and I'm sure it needs it.

I want to thank you rock for taking the time to respond 🤙

 

That's awesome that you found it! Sounds like you helped yourself more than anything I responded with. Good job!

The fuel pumps aren't cheap and you have to make sure you get the right one specific for your truck. I have a ZR2 and they are different than regular Blazers, IIRC. You may never end up needing it if you're buying to put on your shelf just in case. Someone else may have already replaced it.

If you're truck is running well, and you're planning on replacing just for PM, I personally wouldn't.

Full disclosure, though I'm not endorsing buying a fuel pump to keep on the shelf just in case, I bought an AC Delco about 5 years ago when there was a big employee discount day where I worked. Even though I had replaced the pump several years before that. On the shelf it sits and it wouldn't bother me a bit if I never need it.