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1978 300D
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7 Posts
Discussion Starter #1
When cruising on the highway or a secondary road, the engine stays running at high rpm after I let off of the accelerator, even with the dash idle knob set for idle speed. The faster I am cruising, the more noticeable it is. If I shift to neutral, i can hear the engine still revving. After a while it slows down.
The car is a 1978 300D, automatic, with 161,000 miles, I just brought it. I had a vacuum leak on the brown tube, that restored my engine shut-off, locks, and heater functions.
Is there a control for the decel? Also, my idle fluctuates from cold to fully warm engine temp. I have to adjust the dash idle as it warms up. The idle is rough and sometimes stalls. Is there an idle control?
Thanks for any direction.
 

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2001 Volvo V40
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2,954 Posts
The decel is controlled by a two springs on the gas linkage system, one on the firewall and one on the injection pump. All the ball joints of the gas linkage have to be greased, so that it operates smoothly. Check whether the gas linkage reaches the idle and full load stop on the injection pump.

Rough idle can be caused by a variety of things. Have you've done basic maintenance like changed the filter and valve adjustment?
 

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1978 300D
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7 Posts
Discussion Starter #3
I haven't changed the filters or adjusted the valves yet (prev. owner- 30K miles ago). I will be doing all of the maintenance items, now with the shorter days, I am limited to weekend wrenching, I did manage to get a muffler on it and rotate the wheels. I noticed that the #5 glow plug was red hot on the end, until they shut off. I need to clean the interconnections, and I may as well replace the glow plugs while I have the links off. Also I will replace the yellow main vac valve and the transmission dashpot to see if the shifting will occur at the right time, now it has to rev a little higher to shift then what seems normal.
I do have all of the receipts of service from the previous owner for the last 5 years, it helps to see what issues have arose. It seems as though he did not do much to it in the last year, perhaps knowing that he would sell out soon.
 
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