# Could ECU act up intermittently causing high idle? Any other ideas? **URL:** \ **Category:** Maintenance/Repairs\ **Created:** [June 28, 2023, 1:57pm UTC](https://community.cartalk.com/t/could-ecu-act-up-intermittently-causing-high-idle-any-other-ideas/191366 "2023-06-28T13:57:58Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![Jahagafut\_185280](https://avatars.discourse-cdn.com/v4/letter/j/838e76/32.png) [@Jahagafut\_185280](https://community.cartalk.com/u/Jahagafut_185280)\ **Post date:** [June 28, 2023, 1:57pm UTC](https://community.cartalk.com/t/could-ecu-act-up-intermittently-causing-high-idle-any-other-ideas/191366/1 "2023-06-28T13:57:59Z")
I’ve got an 03 Buick Lesabre, 3800 Series II, predictably after an hour of driving the idle starts to get high, it used to go to 3500 but I’ve since replaced the parts I’ll list at the end and it now hangs out around 1800. Sometimes I can sit parked and it goes back to 700 for a minute. If you let it sit turned off it will go back to 700 but quickly start idling high again unless its sat long enough to cool down. I’m thinking either the ECU has circuits that are separating once very heated up, or that there was a leak between the upper intake manifold and the throttle body that opens up under heat, and since I’ve replaced the intake manifold it’s dealt with half of the high idle but the TB is warping under heat, though it’s made of steel and has a brand new gasket. I’ve been to a shop to read live data and he said sensors all look normal but he thinks he hears a vacuum leak but can’t find it listening with a tube and we sprayed lots of brake cleaner everywhere and noticed no different idle from sucking it in. I’ve also played around with the vacuum hoses I could find and hose clamped the slightly warped brake booster line Here’s what I’ve replaced Upper intake manifold and gasket Throttle body gasket and throttle plate cleaning Throttle Position Sensor Idle Air Control Valve MAF sensor MAP sensor PCV Valve Spark plugs Spark plug wires Coil packs Fuel pressure regulator Fuel filter Injectors Trans fluid and filter Air filter Oil and filter Thermostat Radiator cap Engine coolant temperature sensor Removed and cleaned EGR valve Parts I have but haven’t installed: Oil pressure sensor Crankshaft sensor Camshaft sensor O2 sensors There are no OBD codes except when I first got the car there was a stored code for the rear o2 sensor circuit low . ---
**Author:** ![Mustangman](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/mustangman/32/44130_2.png) [@Mustangman](https://community.cartalk.com/u/Mustangman)\ **Post date:** [June 28, 2023, 2:23pm UTC](https://community.cartalk.com/t/could-ecu-act-up-intermittently-causing-high-idle-any-other-ideas/191366/2 "2023-06-28T14:23:22Z")
You are more than halfway to replacing the entire engine’s operating system. Parts tossing is not a substitute for proper diagnosis but you don’t seem to be able to be convinced of this. So why not replace the ECU as well? Good Luck. ---
**Author:** ![Jahagafut\_185280](https://avatars.discourse-cdn.com/v4/letter/j/838e76/32.png) [@Jahagafut\_185280](https://community.cartalk.com/u/Jahagafut_185280)\ **Post date:** [June 28, 2023, 4:14pm UTC](https://community.cartalk.com/t/could-ecu-act-up-intermittently-causing-high-idle-any-other-ideas/191366/3 "2023-06-28T16:14:57Z")
All of that was maintenance I wanted to do with money I had except for the engine coolant temp sensor Leaking intake manifold Dead MAF Seized IAC Original plug wires and coils Black oily plugs Worst air filter I’ve seen Leaking fuel pressure regulator Original PCV MAP was cheap Original trans fluid and filter Plugged fuel filter Filthy throttle body Sticking TPS Original dirty injectors Crank and Camshaft sensors and oil pressure unit six to they cost hardly anything so I bundled them for backups Leaking radiator cap Original thermostat Just because I had the money and wanted to overhaul the engine doesn’t make it not regular maintenance. ---
**Author:** ![Jahagafut\_185280](https://avatars.discourse-cdn.com/v4/letter/j/838e76/32.png) [@Jahagafut\_185280](https://community.cartalk.com/u/Jahagafut_185280)\ **Post date:** [June 28, 2023, 4:16pm UTC](https://community.cartalk.com/t/could-ecu-act-up-intermittently-causing-high-idle-any-other-ideas/191366/4 "2023-06-28T16:16:29Z")
Furthermore the diagnosis at a shop didn’t find anything, they recommended trying a new throttle body and seeing what happens so I’d rather look for other opinions ---
**Author:** ![Jahagafut\_185280](https://avatars.discourse-cdn.com/v4/letter/j/838e76/32.png) [@Jahagafut\_185280](https://community.cartalk.com/u/Jahagafut_185280)\ **Post date:** [June 28, 2023, 4:22pm UTC](https://community.cartalk.com/t/could-ecu-act-up-intermittently-causing-high-idle-any-other-ideas/191366/5 "2023-06-28T16:22:47Z")
I should include it has 250,000km and was not well maintained clearly ---
**Author:** ![Mustangman](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/mustangman/32/44130_2.png) [@Mustangman](https://community.cartalk.com/u/Mustangman)\ **Post date:** [June 28, 2023, 4:24pm UTC](https://community.cartalk.com/t/could-ecu-act-up-intermittently-causing-high-idle-any-other-ideas/191366/6 "2023-06-28T16:24:01Z")
> [@Jahagafut\_185280](#): > > Furthermore the diagnosis at a shop didn’t find anything More than one of us posted the need for a look at “live data” to find the problem. You don’t seem to have the tools to do this and we can’t diagnose the problem without more data. So what do you want? Either change the ECU, which is your idea, or get an new throttle body which is the shop’s suggestion. I’d follow the shop’s suggestion since they actually laid hands on the car. edit… OK 250,000km, yeah, the throttle body may very well be worn out. ---
**Author:** ![Jahagafut\_185280](https://avatars.discourse-cdn.com/v4/letter/j/838e76/32.png) [@Jahagafut\_185280](https://community.cartalk.com/u/Jahagafut_185280)\ **Post date:** [June 28, 2023, 4:26pm UTC](https://community.cartalk.com/t/could-ecu-act-up-intermittently-causing-high-idle-any-other-ideas/191366/7 "2023-06-28T16:26:55Z")
Yeah they looked at live data and couldn’t seem to find anything, he does think it’s possible that the TB and intake manifold were warped and I fixed half the problem by replacing the manifold which was leaking coolant as well, the TB gasket is new and spraying brake clean and wd40 around the area seemed to have no affect on the idle. Maybe it heats up enough after an hour to cause a small leak which is not being registered? You can see the mating surfaces aren’t completely flush in some areas though they don’t look jagged persay ---
**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 28, 2023, 4:32pm UTC](https://community.cartalk.com/t/could-ecu-act-up-intermittently-causing-high-idle-any-other-ideas/191366/8 "2023-06-28T16:32:07Z")
Try unplugging the power steering pressure sensor,(same as a pressure switch), to see if that stabilizes the engine speed. ![image](https://global.discourse-cdn.com/cartalk/original/3X/6/b/6bd7f1335733d4ef7d7438f83904e9231ce1abd8.png) > **[Symptoms of a Bad or Failing Power Steering Pressure Switch | YourMechanic...](https://www.yourmechanic.com/article/symptoms-of-a-bad-or-failing-power-steering-pressure-switch)** > > If you notice your engine slows down, stalls, or speeds up then slows down, have your power steering pressure switch inspected and replaced. Tester ---
**Author:** ![Jahagafut\_185280](https://avatars.discourse-cdn.com/v4/letter/j/838e76/32.png) [@Jahagafut\_185280](https://community.cartalk.com/u/Jahagafut_185280)\ **Post date:** [June 28, 2023, 4:34pm UTC](https://community.cartalk.com/t/could-ecu-act-up-intermittently-causing-high-idle-any-other-ideas/191366/9 "2023-06-28T16:34:22Z")
Ah I misread this, you mean a need to provide live data in the forum before you guys could really help? I thought you said a need to go have livedata read at a shop. I can provide a video of live data this week during the high idle condition if you think this would help the forum help me. ---
**Author:** ![Jahagafut\_185280](https://avatars.discourse-cdn.com/v4/letter/j/838e76/32.png) [@Jahagafut\_185280](https://community.cartalk.com/u/Jahagafut_185280)\ **Post date:** [June 28, 2023, 4:36pm UTC](https://community.cartalk.com/t/could-ecu-act-up-intermittently-causing-high-idle-any-other-ideas/191366/10 "2023-06-28T16:36:07Z")
I will give this a try. I did notice this morning when parking the power steering seemed to stop for a few seconds then return ---
**Author:** ![Mustangman](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/mustangman/32/44130_2.png) [@Mustangman](https://community.cartalk.com/u/Mustangman)\ **Post date:** [June 28, 2023, 4:44pm UTC](https://community.cartalk.com/t/could-ecu-act-up-intermittently-causing-high-idle-any-other-ideas/191366/11 "2023-06-28T16:44:24Z")
You didn’t tell us the shop you used actually captured live data… That just reinforces their suggestion to replace the throttle body. Why do you think that is not a valid suggestion? Again… hands on the car vs random internet forum folks who’ve never even seen your car. ---
**Author:** ![Jahagafut\_185280](https://avatars.discourse-cdn.com/v4/letter/j/838e76/32.png) [@Jahagafut\_185280](https://community.cartalk.com/u/Jahagafut_185280)\ **Post date:** [June 28, 2023, 4:59pm UTC](https://community.cartalk.com/t/could-ecu-act-up-intermittently-causing-high-idle-any-other-ideas/191366/12 "2023-06-28T16:59:35Z")
More so looking for opinions since he just looked at live data and listened around the engine before telling me I could try a TB from a wrecker and if not I could leave it overnight, I had suggested the TB while talking to him and planted it in his head. Should not the idle have changed when spraying brake cleaner around the gasket area or is it possible it is leaking and doing that would have no effect? ---
**Author:** ![NYBo](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/nybo/32/17281_2.png) [@NYBo](https://community.cartalk.com/u/NYBo)\ **Post date:** [June 28, 2023, 5:11pm UTC](https://community.cartalk.com/t/could-ecu-act-up-intermittently-causing-high-idle-any-other-ideas/191366/13 "2023-06-28T17:11:51Z")
Did you spray the ends of the throttle plate shaft? Those are wear points. ---
**Author:** ![Jahagafut\_185280](https://avatars.discourse-cdn.com/v4/letter/j/838e76/32.png) [@Jahagafut\_185280](https://community.cartalk.com/u/Jahagafut_185280)\ **Post date:** [June 28, 2023, 5:14pm UTC](https://community.cartalk.com/t/could-ecu-act-up-intermittently-causing-high-idle-any-other-ideas/191366/14 "2023-06-28T17:14:30Z")
I only sprayed the mating area between the intake and TB. I have had the tb off and cleaned the plate. When idling high moving thy throttle cable around had no effect, is it possible the TB is failing internally when hot and not closing? ---
**Author:** ![TwinTurbo](https://avatars.discourse-cdn.com/v4/letter/t/8baadc/32.png) [@TwinTurbo](https://community.cartalk.com/u/TwinTurbo)\ **Post date:** [June 28, 2023, 5:19pm UTC](https://community.cartalk.com/t/could-ecu-act-up-intermittently-causing-high-idle-any-other-ideas/191366/15 "2023-06-28T17:19:24Z")
Not sure it’s done much anymore but the throttle shaft wears out the bore in the throttle body and creates an air leak. Back in the day, it was fairly common repair to bore out the throttle shaft holes and install bushings to restore the seal between the shaft and throttle body. Probably more cost effective today to replace the assembly… ---
**Author:** ![Jahagafut\_185280](https://avatars.discourse-cdn.com/v4/letter/j/838e76/32.png) [@Jahagafut\_185280](https://community.cartalk.com/u/Jahagafut_185280)\ **Post date:** [June 28, 2023, 5:22pm UTC](https://community.cartalk.com/t/could-ecu-act-up-intermittently-causing-high-idle-any-other-ideas/191366/16 "2023-06-28T17:22:07Z")
Hell I’ll ask the wreckers about throttle body and weigh that option and check that power steering suggestion ---
**Author:** ![TwinTurbo](https://avatars.discourse-cdn.com/v4/letter/t/8baadc/32.png) [@TwinTurbo](https://community.cartalk.com/u/TwinTurbo)\ **Post date:** [June 28, 2023, 5:59pm UTC](https://community.cartalk.com/t/could-ecu-act-up-intermittently-causing-high-idle-any-other-ideas/191366/17 "2023-06-28T17:59:27Z")
You can try wiggling the shaft. If it’s worn too much for the spray to be effective, it will be fairly obvious. If it seems tight in the bores, then try spraying the places on each end where the shaft enters the throttle body as NYBo suggested. See if the RPMs are affected by leaks around the shaft… ---
**Author:** ![Jahagafut\_185280](https://avatars.discourse-cdn.com/v4/letter/j/838e76/32.png) [@Jahagafut\_185280](https://community.cartalk.com/u/Jahagafut_185280)\ **Post date:** [June 28, 2023, 7:59pm UTC](https://community.cartalk.com/t/could-ecu-act-up-intermittently-causing-high-idle-any-other-ideas/191366/18 "2023-06-28T19:59:40Z")
![20230628_135529](https://global.discourse-cdn.com/cartalk/original/3X/3/1/31c9ff48c9a41ae1b70818d2be403bb4121c7778.jpeg) Well I taken it off again to do a second deep cleaning and then lubricate the shaft ---
**Author:** ![George\_San\_Jose1](https://avatars.discourse-cdn.com/v4/letter/g/e5b9ba/32.png) [@George\_San\_Jose1](https://community.cartalk.com/u/George_San_Jose1)\ **Post date:** [June 28, 2023, 10:20pm UTC](https://community.cartalk.com/t/could-ecu-act-up-intermittently-causing-high-idle-any-other-ideas/191366/19 "2023-06-28T22:20:14Z")
In the other thread you said the throttle valve is cable actuated. With that configuration, seems hard to believe a computer fault could cause the 1800 idle rpm. For that high of idle rpm, there has to be a correspondingly large unwanted air path into the intake manifold. Your mechanic apparently tried the tried and true spray-stuff-&-see-if-rpm increases technique to find it in the engine compartment, but didn’t find anything there. Common-sense says an air leak remains, and it must be elsewhere. The primary suspects have to be any tube that connects to the intake manifold. Since not in engine compartment … hmm … - hvac related, vacuum motors under dashboard control hvac doors - Some cars of the past had automatic emergency brakes, activated when transmission in P, powered by engine vacuum. Does your car do anything similar? - Fuel pump related > **[Tech Feature: Returnless Fuel Injection Systems](https://www.brakeandfrontend.com/tech-feature-returnless-fuel-injection-systems/)** > > If you've tried to find the fuel pressure regulator on many late-model engines by looking in the engine compartment, you won't find it there because the regulator has been relocated to the fuel tank. Engines with "returnless" electronic fuel... - Have you tried disabling the engine idle control mechanism? ---
**Author:** ![Jahagafut\_185280](https://avatars.discourse-cdn.com/v4/letter/j/838e76/32.png) [@Jahagafut\_185280](https://community.cartalk.com/u/Jahagafut_185280)\ **Post date:** [June 28, 2023, 11:42pm UTC](https://community.cartalk.com/t/could-ecu-act-up-intermittently-causing-high-idle-any-other-ideas/191366/20 "2023-06-28T23:42:27Z")
I do not have the parking brake mechanism, I’ve tried unplugging the idle air control during the issue but I guess that would be no help, during tb cleaning I made sure to pay focus to that port though and lubricate it will to ensure the IAC can fully plunge out at all times. I have read about someone having this same issue due to fuel pump, I’ve tried tapping around the fuel pump during but that’s hardly a accurate test. I’ve also sprayed around every port into the intake manifold, around brake booster and pretty much anywhere visible to me that could have a vacuum leak. I’m really hoping that the tb wasn’t evenly torqued since when I reinstalled it out was after hours of messing around with the manifold and I thin I may have been in a rush to reattach the tb [Next page](https://community.cartalk.com/t/could-ecu-act-up-intermittently-causing-high-idle-any-other-ideas/191366.md?page=2)