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 .
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.
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.
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
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.
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
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.
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?
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?
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…
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…
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
Have you tried disabling the engine idle control mechanism?
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
