# 2002 GMC Sierra 1500 - Slightly fluctuating RPMs **URL:** \ **Category:** Maintenance/Repairs\ **Tags:** sierra-1500, gmc\ **Created:** [June 12, 2020, 3:00pm UTC](https://community.cartalk.com/t/2002-gmc-sierra-1500-slightly-fluctuating-rpms/165680 "2020-06-12T15:00:41Z")\ **Posts on this page:** 11\ **Page:** 1
**Author:** ![David5292\_150742](https://avatars.discourse-cdn.com/v4/letter/d/77aa72/32.png) [@David5292\_150742](https://community.cartalk.com/u/David5292_150742)\ **Post date:** [June 12, 2020, 3:00pm UTC](https://community.cartalk.com/t/2002-gmc-sierra-1500-slightly-fluctuating-rpms/165680/1 "2020-06-12T15:00:41Z")
I have a 2002 GMC sierra 1500, V6 4.3L. I am having an issue with the RPMs slightly fluctuating when accelerating. It does not seem to do it all the time. Or eventually it will go away for a while and come back when driving for a while. The RPMs generally only jump up an down less than 100 RPM or so (it moves very little). You can actually feel the trucks RPM changing so not a gauge issue. I don’t think it fluctuates when idle (at least I don’t see it), mostly just during acceleration, when speeding up its hard to notice, its usually when you are driving steady. I tend to mostly see it in 3rd gear, but I believe it does it in every gear, just not as noticeable. Transmission also seems to shift fine. There are is no check engine light, and no codes. Recently had a tuneup done, new plugs and wires, so no misfiring. Replaced both catalytic converters. I will be installing a new fuel filter soon, so may see if that does anything. Things I suspect may be issue: - Fuel filter – will replace soon - Throttle body/Sensor – will try to clean it and test the sensor for resistance - MAF Sensor – will try to clean it - Transmission/Converter - Exhaust leak – haven’t checked yet Any ideas what could be wrong? ---
**Author:** ![old\_mopar\_guy](https://avatars.discourse-cdn.com/v4/letter/o/6bbea6/32.png) [@old\_mopar\_guy](https://community.cartalk.com/u/old_mopar_guy)\ **Post date:** [June 12, 2020, 3:16pm UTC](https://community.cartalk.com/t/2002-gmc-sierra-1500-slightly-fluctuating-rpms/165680/2 "2020-06-12T15:16:14Z")
Absolutely nothing is probably wrong. Don’t go looking to fix what isn’t broken. A slight (100 rpm) fluctuation could simply be normal engagement/disengagement of the a/c clutch. ---
**Author:** ![Barkydog](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/barkydog/32/2470_2.png) [@Barkydog](https://community.cartalk.com/u/Barkydog)\ **Post date:** [June 12, 2020, 3:32pm UTC](https://community.cartalk.com/t/2002-gmc-sierra-1500-slightly-fluctuating-rpms/165680/3 "2020-06-12T15:32:39Z")
Does it only do it when the ac is on? ---
**Author:** ![David5292\_150742](https://avatars.discourse-cdn.com/v4/letter/d/77aa72/32.png) [@David5292\_150742](https://community.cartalk.com/u/David5292_150742)\ **Post date:** [June 12, 2020, 7:08pm UTC](https://community.cartalk.com/t/2002-gmc-sierra-1500-slightly-fluctuating-rpms/165680/5 "2020-06-12T19:08:18Z")
If it was the A/C clutch; wouldn’t it do it just when the a/c is on? Mine fluctuates regardless of a/c being on or off, and it revs up and down continuously for almost the entire drive. Sometimes it doesn’t do it at all. ---
**Author:** ![David5292\_150742](https://avatars.discourse-cdn.com/v4/letter/d/77aa72/32.png) [@David5292\_150742](https://community.cartalk.com/u/David5292_150742)\ **Post date:** [June 12, 2020, 7:08pm UTC](https://community.cartalk.com/t/2002-gmc-sierra-1500-slightly-fluctuating-rpms/165680/6 "2020-06-12T19:08:51Z")
It does it regardless whether a/c is on or not. You can literally feel the truck hestitate or rev up and down when driving ---
**Author:** ![Tester](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/tester/32/15976_2.png) [@Tester](https://community.cartalk.com/u/Tester)\ **Post date:** [June 12, 2020, 7:25pm UTC](https://community.cartalk.com/t/2002-gmc-sierra-1500-slightly-fluctuating-rpms/165680/7 "2020-06-12T19:25:25Z")
Have the fuel pressure tested. Your vehicle uses CPI fuel system. This means there’s a component under the intake manifold called the spider assembly. ![image](https://global.discourse-cdn.com/cartalk/original/3X/6/b/6b069eda257e85d342ad83dbdca463c74eff41b8.jpeg) The spider assembly relies on the fuel pressure to blow open the poppet valves at the injectors. Tester ---
**Author:** ![Bugmenot](https://avatars.discourse-cdn.com/v4/letter/b/7c8e57/32.png) [@Bugmenot](https://community.cartalk.com/u/Bugmenot)\ **Post date:** [June 12, 2020, 7:31pm UTC](https://community.cartalk.com/t/2002-gmc-sierra-1500-slightly-fluctuating-rpms/165680/8 "2020-06-12T19:31:14Z")
What you are describing sounds like “surging”. There is any number of causes. A mechanic will have to go through a diagnostic procedure. Following is the procedure from the service manual (click to blow up). ![2002 GMC Surging](https://global.discourse-cdn.com/cartalk/original/3X/a/b/ab0577e55aef85d6712087d70aca31f4035347ff.png) I once experienced surging in a 1994 Chevy S10 at steady speed on the highway. The problem turned out to be a partly fouled spark plug. Probably not the problem here since the plugs have been replaced. ---
**Author:** ![David5292\_150742](https://avatars.discourse-cdn.com/v4/letter/d/77aa72/32.png) [@David5292\_150742](https://community.cartalk.com/u/David5292_150742)\ **Post date:** [June 12, 2020, 7:54pm UTC](https://community.cartalk.com/t/2002-gmc-sierra-1500-slightly-fluctuating-rpms/165680/9 "2020-06-12T19:54:20Z")
I have already replaced spider injector, maybe will try some injector cleaner or something. I am also going to be installing a fuel filter in a few days to see if that helps. ---
**Author:** ![David5292\_150742](https://avatars.discourse-cdn.com/v4/letter/d/77aa72/32.png) [@David5292\_150742](https://community.cartalk.com/u/David5292_150742)\ **Post date:** [June 12, 2020, 7:57pm UTC](https://community.cartalk.com/t/2002-gmc-sierra-1500-slightly-fluctuating-rpms/165680/10 "2020-06-12T19:57:32Z")
Yea, I recently just replaced them, maybe a few months ago with ACdelco plugs/wires. Might still check to see if they are arcing or something sometimes. Not sure if it is related, but the fuel gauge isn’t accurate sometimes. I’ll drive and all of a sudden it drops a little and raises back up. It doesn’t do it all the time either. It doesn’t seem to do it when the RPM fluctuates. ---
**Author:** ![Bugmenot](https://avatars.discourse-cdn.com/v4/letter/b/7c8e57/32.png) [@Bugmenot](https://community.cartalk.com/u/Bugmenot)\ **Post date:** [June 12, 2020, 8:13pm UTC](https://community.cartalk.com/t/2002-gmc-sierra-1500-slightly-fluctuating-rpms/165680/11 "2020-06-12T20:13:46Z")
Check the electrical connector at the fuel pump module for corrosion. Poor connections could cause intermittent issues with the fuel level sender and/or the fuel pump/fuel pressure. ---
**Author:** ![shanonia](https://avatars.discourse-cdn.com/v4/letter/s/9de053/32.png) [@shanonia](https://community.cartalk.com/u/shanonia)\ **Post date:** [June 12, 2020, 8:20pm UTC](https://community.cartalk.com/t/2002-gmc-sierra-1500-slightly-fluctuating-rpms/165680/12 "2020-06-12T20:20:14Z")
I had similar, maybe not so pronounced, symptoms on my Chrysler minivan. Was also losing coolant slowly. Did a pressure test on the cooling system and found a leaking intake manifold gasket. Fixed that and the engine runs smoothly again.