Intermittent high idle after TPS replacement.

[Green57]

The idle in my SVO has been sticking at 2000 rpms after the car warmed up. This has been happening for a few weeks, so I figured it was time for a new TPS. While installing the new TPS I also cleaned my IAC, throttle body and EGR. I put it all back together with new gaskets, and reset the base idle and timing. I set the new TPS at .984 volts at idle up to above 4.75 at WOT.

I took the car out for a test drive and everything seemed to be working fine except every now and then when I let off the throttle the idle would go up to about 2100 then come down and hold at 2000. A quick tap on the throttle and the idle would drop back to normal. Before the new TPS tapping on the throttle would not help…so at least now it will go back to idle, but it still is not correct.

I thought there might be something else wrong so I pulled these codes when I returned from the test drive.

I have an early 85 all stock except for a LA3 with after market 35 pound injectors, and a 3" down pipe.

KOEO

54 ACT or VAT sensor signal voltage is to high.
81 Boost solenoid - circuit failure. I have a manual boost controller so that would make sense.
82 Electro - Drive Fan: circuit failure. I did notice the fan did not turn on after the gauge was reading to the high side of normal.
83 could be EGR or fan. Not quite sure about that one.

KOER

24 ACT or VAT not at normal levels.
25 KS not detected during Engine Run Self-Test
34 EGR Pressure Feedback signal voltage out of limits or insufficient EGR flow
75 Brake on/off switch always closed circuit. No worries on this one.

Would the 54 and 24 VAT codes cause idle problems?

Not quite sure what to do, any help or ideas for a repair?

Thank you,

G57

[svono50]

In short, yes the 54/24 codes can effect your idle. The LA3 computer is a bit different than the SVO EEC's as in it has two air temp sensors, the VAT in the VAF and the ACT in the lower intake runner as you likely already know. Both sensors are thermistor type, where the voltage output drops with temp increase. So if the EEC sees a warm engine coolant sensor and a really high VAT/ACT it thinks that there is something wrong with one or both of the sensors. You would need to either check the voltage on the output of both sensors with KOEO or see what the resistance across the sensors is and see if they match the recommended values. If you don't have a reference on those, let me know and I can scan them in for you.

Another cause could be worn linkage connections on the throttle body itself. When you slowly let off the throttle the throttle plate shaft doesn't fully return to the closed position and because of the linkage slop the main arm doesn't push on it. A quick snap of the throttle will give it enough momentum to snap fully closed and bring the idle back down. I have had this issue with mine for years and have been too lazy to do anything about it. Something else to look at.

[Green57]

svono50,

Thank you for the reply. Since I don't have the ACT installed in the intake I thought the 54/24 codes were given because the computer is not receiving an input signal from that sensor, but I'm not sure.

Does anyone have a reference of codes that can be normally disregarded after doing a LA3 swap? I kind of miss getting the 11s when everything is working correctly. When I get some of the codes from the LA3 I'm not sure what is legit and what is not.

I've been told that I can adjust the TPS to the lower side, as close to .90 as possible and that should help. I'll let you if it works for me.

G57

[SVOeric]

Remember, when you adjust the TPS, you have to go through the idle set procedure again.

This does look to be an ACT code I believe. it's really hard to tell which code is the actual sensor in the VAM, and which one is the ACT, but I do believe this is the ACT.

[GAboySVO]

Did you verify the new TPS sensor's functionality with a voltmeter? New doesn't always mean good.

[Green57]

I set the TPS to .902 but I still get the high idle every now and then. Its usually when I'm driving at slower speeds like in a school zone or parking lot. A blip to the throttle drops it back to normal, its just annoying. I don't know where to go from here. Is there an after market throttle body that fits the SVO intake?

GAboySVO, yes I did check the TPS after I set it. There were no dead spots that I could see. I used a digital volt meter to check it, the numbers increased at a normal pace with no erratic behavior. I will check it again with my analog meter if you think its necessary.

On a side note it seems that the milage is not back to where it should be. Normally I get around 280 miles a tank normal driving, around 305 highway. I thought with the new TPS it would go back to normal, but it looks like I'm coming up short again.

Is there another sensor that would effect the cars idle and gas milage? All the sensors are original except the O2 sensor and the fuel pressure regulator they were replaced in 2007.

Thanks again for any help.

G57

[MAPSVO]

I had a similar condition with my 86. After warm up while sitting a stoplight sometimes the idle would go from about 900 to about 1500 without touching the gas pedal, a quick blip would not affect it, however if you turned the car off and restarted it would be back down to 900. This was intermittent and did not always happen. I had already changed the TPS, reset the base idle and replaced the IAC motor/valve. I even chased down the seal for the throttle shaft and replaced it.

After some study I learned the O2 sensor is what I think was called a "closed loop" system and the EEC depended on a signal or a series of signals to keep from going to the cold idle mode. I replaced the O2 sensor and it seemed to fix the issue. My other option was the coolant temp sensor which I believe also feeds a signal to the EEC. That would have been my next step.

Now, my car had been in storage this past winter since about October, I replaced the O2 sensor in April, but had not driven the car until my son-in law drove it to a cruise two weeks ago. He told me the throttle was sticking at about 2000-2500 RPM, and he about ruined the clutch in the process. That was my fault for not driving the car myself the first time out. Anyway I drove it back to our storage building and put it away for a week. I went down there last weekend to investigate the problem. It turned out that the throttle cable was apparently frayed and probably rusted inside the sleeve at the throttle body. It was actually making a grinding noise and was hanging at about 2500RPM unless you manually forced the throttle shaft closed.

So I had the first issue which I think is fixed and the second was probably due the old cable that had sit for several months without being used.

I have a new cable on the way. Sorry for the long post but in case your high idle is associated with pedal movement and not all by itself unhook the cable and check it out.

Mark

[svono50]

Mark, good info! I was going to mention the coolant sensor (ECT) that is located in the top/middle of the lower intake manifold between injectors #2 & 3. That sensor would make my idle jump up to 2000rpm and sometimes higher randomly and no amount of blipping the throttle would bring it back down, only an ignition reset. When the sensor goes 'bad' the EEC defaults to below zero for estimated temp and shoots the fast idle routine. That can be tested by measuring the resistance across the sensor's two terminals with the harness disconnected. This would certainly kill your mileage.

[Green57]

Mark, Thank you for your input. I have checked the cable. I installed a new hood pad from a 89 and there were two places were the linkage was rubbing the new pad. I though it would be strange for the pad to make the throttle stick at 2000 rpms, but looked into it any way. I opened up both holes to make sure there was plenty of room for the linkage to move. Cable moves freely from idle to WOT.

svono50, ECT will be next on my list. It is twenty-nine years old, so It can't hurt to change it.

I installed a Bosh 02 sensor in 2007, do they go bad that quickly? Will the LA3 computer give a code for a bad O2 sensor?

G57

[MAPSVO]

I had a new Bosch O2 sensor on my car and it was only 2 years old. I put another one just like it on. I'm still not 100% sure it is fixed. I will install the new throttle cable today and it's a 120 mile trip back so by the time I get home I should know. My hood pad is one of those generic types that I got from NPD, the linkage was rubbing into the pad so cut a small rectangle in the pad to make sure it didn't cause a problem.

Good luck to the both of us

Report from trip home, the idle issue seems to be cured, when cold it goes up to about 12-1300 and gradually goes down. When fully warmed up it is at 900. The throttle cable works well also